[v4,2/2] mm/hmm/test: add self tests for HMM
diff mbox series

Message ID 20191104222141.5173-3-rcampbell@nvidia.com
State New
Headers show
Series
  • HMM tests and minor fixes
Related show

Commit Message

Ralph Campbell Nov. 4, 2019, 10:21 p.m. UTC
Add self tests for HMM.

Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
---
 MAINTAINERS                            |    3 +
 include/uapi/linux/test_hmm.h          |   59 ++
 lib/Kconfig.debug                      |   11 +
 lib/Makefile                           |    1 +
 lib/test_hmm.c                         | 1306 ++++++++++++++++++++++++
 tools/testing/selftests/vm/.gitignore  |    1 +
 tools/testing/selftests/vm/Makefile    |    3 +
 tools/testing/selftests/vm/config      |    2 +
 tools/testing/selftests/vm/hmm-tests.c | 1295 +++++++++++++++++++++++
 tools/testing/selftests/vm/run_vmtests |   16 +
 tools/testing/selftests/vm/test_hmm.sh |   97 ++
 11 files changed, 2794 insertions(+)
 create mode 100644 include/uapi/linux/test_hmm.h
 create mode 100644 lib/test_hmm.c
 create mode 100644 tools/testing/selftests/vm/hmm-tests.c
 create mode 100755 tools/testing/selftests/vm/test_hmm.sh

Comments

Christoph Hellwig Nov. 12, 2019, 3:25 p.m. UTC | #1
Shouldn't this go into mm/ instead? It certainly doesn't seem
like a library.

> +static int dmirror_bounce_copy_from(struct dmirror_bounce *bounce,
> +				    unsigned long addr)
> +{
> +	unsigned long end = addr + bounce->size;
> +	char __user *uptr = (void __user *)addr;
> +	void *ptr = bounce->ptr;
> +
> +	for (; addr < end; addr += PAGE_SIZE, ptr += PAGE_SIZE,
> +					      uptr += PAGE_SIZE) {
> +		int ret;
> +
> +		ret = copy_from_user(ptr, uptr, PAGE_SIZE);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}

Why does this iterate in page sized chunks?  I don't remember a page
size limit on copy_{from,to}_user.

> +static int dmirror_invalidate_range_start(struct mmu_notifier *mn,
> +				const struct mmu_notifier_range *update)
> +{
> +	struct dmirror *dmirror = container_of(mn, struct dmirror, notifier);
> +
> +	if (mmu_notifier_range_blockable(update))
> +		mutex_lock(&dmirror->mutex);
> +	else if (!mutex_trylock(&dmirror->mutex))
> +		return -EAGAIN;
> +
> +	dmirror_do_update(dmirror, update->start, update->end);
> +	mutex_unlock(&dmirror->mutex);
> +	return 0;
> +}

Can we adopts this to Jasons new interval tree invalidate?

> +static int dmirror_fops_open(struct inode *inode, struct file *filp)
> +{
> +	struct cdev *cdev = inode->i_cdev;
> +	struct dmirror_device *mdevice;
> +	struct dmirror *dmirror;
> +
> +	/* No exclusive opens. */
> +	if (filp->f_flags & O_EXCL)
> +		return -EINVAL;

Device files usually just ignore O_EXCL, I don't see why this one
would be any different.

> +	mdevice = container_of(cdev, struct dmirror_device, cdevice);
> +	dmirror = dmirror_new(mdevice);
> +	if (!dmirror)
> +		return -ENOMEM;
> +
> +	/* Only the first open registers the address space. */
> +	mutex_lock(&mdevice->devmem_lock);
> +	if (filp->private_data)
> +		goto err_busy;
> +	filp->private_data = dmirror;
> +	mutex_unlock(&mdevice->devmem_lock);

->open is only called for the first open of a given file structure..

> +static int dmirror_fops_release(struct inode *inode, struct file *filp)
> +{
> +	struct dmirror *dmirror = filp->private_data;
> +
> +	if (!dmirror)
> +		return 0;

This can't happen if your ->open never returns 0 without setting the
private data.

> +	filp->private_data = NULL;

The file is feed afterwards, no need to clear the private data.
Ralph Campbell Nov. 12, 2019, 9:51 p.m. UTC | #2
On 11/12/19 7:25 AM, Christoph Hellwig wrote:
> Shouldn't this go into mm/ instead? It certainly doesn't seem
> like a library.

I was following the convention for the other vm test kernel modules.
I see a couple of modules in mm/ but I don't have a personal
preference for where to place it.

Andrew, do you have a preference?

>> +static int dmirror_bounce_copy_from(struct dmirror_bounce *bounce,
>> +				    unsigned long addr)
>> +{
>> +	unsigned long end = addr + bounce->size;
>> +	char __user *uptr = (void __user *)addr;
>> +	void *ptr = bounce->ptr;
>> +
>> +	for (; addr < end; addr += PAGE_SIZE, ptr += PAGE_SIZE,
>> +					      uptr += PAGE_SIZE) {
>> +		int ret;
>> +
>> +		ret = copy_from_user(ptr, uptr, PAGE_SIZE);
>> +		if (ret)
>> +			return ret;
>> +	}
>> +
>> +	return 0;
>> +}
> 
> Why does this iterate in page sized chunks?  I don't remember a page
> size limit on copy_{from,to}_user.

Good point. I'll fix that.

>> +static int dmirror_invalidate_range_start(struct mmu_notifier *mn,
>> +				const struct mmu_notifier_range *update)
>> +{
>> +	struct dmirror *dmirror = container_of(mn, struct dmirror, notifier);
>> +
>> +	if (mmu_notifier_range_blockable(update))
>> +		mutex_lock(&dmirror->mutex);
>> +	else if (!mutex_trylock(&dmirror->mutex))
>> +		return -EAGAIN;
>> +
>> +	dmirror_do_update(dmirror, update->start, update->end);
>> +	mutex_unlock(&dmirror->mutex);
>> +	return 0;
>> +}
> 
> Can we adopts this to Jasons new interval tree invalidate?

Well, it would mean registering for the whole process address space.
I'll give it a try.

>> +static int dmirror_fops_open(struct inode *inode, struct file *filp)
>> +{
>> +	struct cdev *cdev = inode->i_cdev;
>> +	struct dmirror_device *mdevice;
>> +	struct dmirror *dmirror;
>> +
>> +	/* No exclusive opens. */
>> +	if (filp->f_flags & O_EXCL)
>> +		return -EINVAL;
> 
> Device files usually just ignore O_EXCL, I don't see why this one
> would be any different.

OK, I'll remove that test.

>> +	mdevice = container_of(cdev, struct dmirror_device, cdevice);
>> +	dmirror = dmirror_new(mdevice);
>> +	if (!dmirror)
>> +		return -ENOMEM;
>> +
>> +	/* Only the first open registers the address space. */
>> +	mutex_lock(&mdevice->devmem_lock);
>> +	if (filp->private_data)
>> +		goto err_busy;
>> +	filp->private_data = dmirror;
>> +	mutex_unlock(&mdevice->devmem_lock);
> 
> ->open is only called for the first open of a given file structure..
> 
>> +static int dmirror_fops_release(struct inode *inode, struct file *filp)
>> +{
>> +	struct dmirror *dmirror = filp->private_data;
>> +
>> +	if (!dmirror)
>> +		return 0;
> 
> This can't happen if your ->open never returns 0 without setting the
> private data.
> 
>> +	filp->private_data = NULL;
> 
> The file is feed afterwards, no need to clear the private data.

OK, I'll clean that up.
Jason Gunthorpe Nov. 12, 2019, 11:45 p.m. UTC | #3
On Tue, Nov 12, 2019 at 01:51:11PM -0800, Ralph Campbell wrote:

> > > +static int dmirror_invalidate_range_start(struct mmu_notifier *mn,
> > > +				const struct mmu_notifier_range *update)
> > > +{
> > > +	struct dmirror *dmirror = container_of(mn, struct dmirror, notifier);
> > > +
> > > +	if (mmu_notifier_range_blockable(update))
> > > +		mutex_lock(&dmirror->mutex);
> > > +	else if (!mutex_trylock(&dmirror->mutex))
> > > +		return -EAGAIN;
> > > +
> > > +	dmirror_do_update(dmirror, update->start, update->end);
> > > +	mutex_unlock(&dmirror->mutex);
> > > +	return 0;
> > > +}
> > 
> > Can we adopts this to Jasons new interval tree invalidate?
> 
> Well, it would mean registering for the whole process address space.
> I'll give it a try.

I'm not sure it makes much sense that this testing is essentially
modeled after nouveau's usage which is very strange compared to the
other drivers.

Jason
Andrew Morton Nov. 13, 2019, 12:08 a.m. UTC | #4
On Tue, 12 Nov 2019 13:51:11 -0800 Ralph Campbell <rcampbell@nvidia.com> wrote:

> On 11/12/19 7:25 AM, Christoph Hellwig wrote:
> > Shouldn't this go into mm/ instead? It certainly doesn't seem
> > like a library.
> 
> I was following the convention for the other vm test kernel modules.
> I see a couple of modules in mm/ but I don't have a personal
> preference for where to place it.
> 
> Andrew, do you have a preference?

q:/usr/src/25> ls -l lib/test_*.c|wc 
     33     297    2051

lib/ is a somewhat strange place, but I'd use that for now.

Presumably one day someone will (pointlessly) move these into
lib/test-modules/.

Then into lib/test-modules/mm/, etc..
Christoph Hellwig Nov. 13, 2019, 1:51 p.m. UTC | #5
On Tue, Nov 12, 2019 at 11:45:52PM +0000, Jason Gunthorpe wrote:
> > Well, it would mean registering for the whole process address space.
> > I'll give it a try.
> 
> I'm not sure it makes much sense that this testing is essentially
> modeled after nouveau's usage which is very strange compared to the
> other drivers.

Which means we really should make the test cases fit the proper usage.
Maybe defer the tests for 5.5 and just merge the first patch for now?
Ralph Campbell Nov. 14, 2019, 11:06 p.m. UTC | #6
On 11/13/19 5:51 AM, Christoph Hellwig wrote:
> On Tue, Nov 12, 2019 at 11:45:52PM +0000, Jason Gunthorpe wrote:
>>> Well, it would mean registering for the whole process address space.
>>> I'll give it a try.
>>
>> I'm not sure it makes much sense that this testing is essentially
>> modeled after nouveau's usage which is very strange compared to the
>> other drivers.
> 
> Which means we really should make the test cases fit the proper usage.
> Maybe defer the tests for 5.5 and just merge the first patch for now?
> 

I think this a good point to discuss.
Some devices will want to register for all changes to the process address
space because there is no requirement to preregister regions that the
device can access verses devices like InfiniBand where a range of addresses
have to be registered before the device can access those addresses.
So for nouveau and the hmm-test driver, the mmu_range_notifier_insert()
and mmu_range_notifier_remove() are only used long enough to get a
stable copy of a small part of the process address space and copy it to
the device's page table. Then the regular process wide invalidations are
required to keep the device's page tables consistent with the process
page table.

The "hacky" part of the current design is the interaction between the
short term narrow address range invalidations verses the long term
process wide invalidations. (double callbacks, double locking of the
device page table)

Both types of invalidate callbacks seem useful to me so forcing a
driver to use only one type doesn't make sense to me.
Jason Gunthorpe Nov. 15, 2019, 2:06 p.m. UTC | #7
On Thu, Nov 14, 2019 at 03:06:05PM -0800, Ralph Campbell wrote:
> 
> On 11/13/19 5:51 AM, Christoph Hellwig wrote:
> > On Tue, Nov 12, 2019 at 11:45:52PM +0000, Jason Gunthorpe wrote:
> > > > Well, it would mean registering for the whole process address space.
> > > > I'll give it a try.
> > > 
> > > I'm not sure it makes much sense that this testing is essentially
> > > modeled after nouveau's usage which is very strange compared to the
> > > other drivers.
> > 
> > Which means we really should make the test cases fit the proper usage.
> > Maybe defer the tests for 5.5 and just merge the first patch for now?
> > 
> 
> I think this a good point to discuss.
> Some devices will want to register for all changes to the process address
> space because there is no requirement to preregister regions that the
> device can access verses devices like InfiniBand where a range of addresses
> have to be registered before the device can access those addresses.

But this is a very bad idea to register and do HW actions for ranges
that can't possibly have any pages registered. It slows down the
entire application

I think the ODP approach might be saner, when it mirrors the entire
address space it chops it up into VA chunks, and once a page is
registered on the HW the VA chunk goes into the interval tree.

Presumably the GPU also has some kind of page table tree and you could
set one of the levels as the VA interval when there are populated children

Jason
Ralph Campbell Nov. 18, 2019, 6:32 p.m. UTC | #8
On 11/15/19 6:06 AM, Jason Gunthorpe wrote:
> On Thu, Nov 14, 2019 at 03:06:05PM -0800, Ralph Campbell wrote:
>>
>> On 11/13/19 5:51 AM, Christoph Hellwig wrote:
>>> On Tue, Nov 12, 2019 at 11:45:52PM +0000, Jason Gunthorpe wrote:
>>>>> Well, it would mean registering for the whole process address space.
>>>>> I'll give it a try.
>>>>
>>>> I'm not sure it makes much sense that this testing is essentially
>>>> modeled after nouveau's usage which is very strange compared to the
>>>> other drivers.
>>>
>>> Which means we really should make the test cases fit the proper usage.
>>> Maybe defer the tests for 5.5 and just merge the first patch for now?
>>>
>>
>> I think this a good point to discuss.
>> Some devices will want to register for all changes to the process address
>> space because there is no requirement to preregister regions that the
>> device can access verses devices like InfiniBand where a range of addresses
>> have to be registered before the device can access those addresses.
> 
> But this is a very bad idea to register and do HW actions for ranges
> that can't possibly have any pages registered. It slows down the
> entire application
> 
> I think the ODP approach might be saner, when it mirrors the entire
> address space it chops it up into VA chunks, and once a page is
> registered on the HW the VA chunk goes into the interval tree.
> 
> Presumably the GPU also has some kind of page table tree and you could
> set one of the levels as the VA interval when there are populated children
> 
> Jason

I wasn't suggesting that HW invalidates happen in two places.
I'm suggesting the two styles of invalidates can work together.
For example, what if a driver calls mmu_notifier_register(mn, mm)
to register for address space wide invalidations, then some time
later there is a device page table fault and the driver calls
mmu_range_notifier_insert() but with a NULL ops.invalidate.
The fault handler follows the nouveau/test_hmm pattern to call
     mmu_range_read_begin()
     hmm_range_fault()
     device lock
     mmu_range_read_retry()
     update device page tables
     device unlock
     mmu_range_notifier_remove()

The global invalidate() callback would get the device lock and
call into mm to update the sequence number of any affected ranges
instead of having a range invalidate callback, and then do the HW
invalidations.
Jason Gunthorpe Nov. 18, 2019, 6:42 p.m. UTC | #9
On Mon, Nov 18, 2019 at 10:32:18AM -0800, Ralph Campbell wrote:
> 
> On 11/15/19 6:06 AM, Jason Gunthorpe wrote:
> > On Thu, Nov 14, 2019 at 03:06:05PM -0800, Ralph Campbell wrote:
> > > 
> > > On 11/13/19 5:51 AM, Christoph Hellwig wrote:
> > > > On Tue, Nov 12, 2019 at 11:45:52PM +0000, Jason Gunthorpe wrote:
> > > > > > Well, it would mean registering for the whole process address space.
> > > > > > I'll give it a try.
> > > > > 
> > > > > I'm not sure it makes much sense that this testing is essentially
> > > > > modeled after nouveau's usage which is very strange compared to the
> > > > > other drivers.
> > > > 
> > > > Which means we really should make the test cases fit the proper usage.
> > > > Maybe defer the tests for 5.5 and just merge the first patch for now?
> > > > 
> > > 
> > > I think this a good point to discuss.
> > > Some devices will want to register for all changes to the process address
> > > space because there is no requirement to preregister regions that the
> > > device can access verses devices like InfiniBand where a range of addresses
> > > have to be registered before the device can access those addresses.
> > 
> > But this is a very bad idea to register and do HW actions for ranges
> > that can't possibly have any pages registered. It slows down the
> > entire application
> > 
> > I think the ODP approach might be saner, when it mirrors the entire
> > address space it chops it up into VA chunks, and once a page is
> > registered on the HW the VA chunk goes into the interval tree.
> > 
> > Presumably the GPU also has some kind of page table tree and you could
> > set one of the levels as the VA interval when there are populated children
> > 
> > Jason
> 
> I wasn't suggesting that HW invalidates happen in two places.
> I'm suggesting the two styles of invalidates can work together.
> For example, what if a driver calls mmu_notifier_register(mn, mm)
> to register for address space wide invalidations, then some time
> later there is a device page table fault and the driver calls
> mmu_range_notifier_insert() but with a NULL ops.invalidate.

I'm saying drivers shouldn't do that, it is a basically a hack that it
works at all.

> The global invalidate() callback would get the device lock and
> call into mm to update the sequence number of any affected ranges
> instead of having a range invalidate callback, and then do the HW
> invalidations.

No, I just finished eliminating all the range iteration code in the
drivers - and you can't update the sequence number from any place
other than the interval invalidation callback anyhow.

Jason

Patch
diff mbox series

diff --git a/MAINTAINERS b/MAINTAINERS
index c6c34d04ce95..8d53e39df193 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7428,7 +7428,10 @@  L:	linux-mm@kvack.org
 S:	Maintained
 F:	mm/hmm*
 F:	include/linux/hmm*
+F:	include/uapi/linux/test_hmm*
 F:	Documentation/vm/hmm.rst
+F:	lib/test_hmm*
+F:	tools/testing/selftests/vm/*hmm*
 
 HOST AP DRIVER
 M:	Jouni Malinen <j@w1.fi>
diff --git a/include/uapi/linux/test_hmm.h b/include/uapi/linux/test_hmm.h
new file mode 100644
index 000000000000..8c5f70c160bf
--- /dev/null
+++ b/include/uapi/linux/test_hmm.h
@@ -0,0 +1,59 @@ 
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * This is a module to test the HMM (Heterogeneous Memory Management) API
+ * of the kernel. It allows a userspace program to expose its entire address
+ * space through the HMM test module device file.
+ */
+#ifndef _UAPI_LINUX_HMM_DMIRROR_H
+#define _UAPI_LINUX_HMM_DMIRROR_H
+
+#include <linux/types.h>
+#include <linux/ioctl.h>
+
+/*
+ * Structure to pass to the HMM test driver to mimic a device accessing
+ * system memory and ZONE_DEVICE private memory through device page tables.
+ *
+ * @addr: (in) user address the device will read/write
+ * @ptr: (in) user address where device data is copied to/from
+ * @npages: (in) number of pages to read/write
+ * @cpages: (out) number of pages copied
+ * @faults: (out) number of device page faults seen
+ */
+struct hmm_dmirror_cmd {
+	__u64		addr;
+	__u64		ptr;
+	__u64		npages;
+	__u64		cpages;
+	__u64		faults;
+};
+
+/* Expose the address space of the calling process through hmm device file */
+#define HMM_DMIRROR_READ		_IOWR('H', 0x00, struct hmm_dmirror_cmd)
+#define HMM_DMIRROR_WRITE		_IOWR('H', 0x01, struct hmm_dmirror_cmd)
+#define HMM_DMIRROR_MIGRATE		_IOWR('H', 0x02, struct hmm_dmirror_cmd)
+#define HMM_DMIRROR_SNAPSHOT		_IOWR('H', 0x03, struct hmm_dmirror_cmd)
+
+/*
+ * Values returned in hmm_dmirror_cmd.ptr for HMM_DMIRROR_SNAPSHOT.
+ * HMM_DMIRROR_PROT_ERROR: no valid mirror PTE for this page
+ * HMM_DMIRROR_PROT_NONE: unpopulated PTE or PTE with no access
+ * HMM_DMIRROR_PROT_READ: read-only PTE
+ * HMM_DMIRROR_PROT_WRITE: read/write PTE
+ * HMM_DMIRROR_PROT_ZERO: special read-only zero page
+ * HMM_DMIRROR_PROT_DEV_PRIVATE_LOCAL: Migrated device private page on the
+ *					device the ioctl() is made
+ * HMM_DMIRROR_PROT_DEV_PRIVATE_REMOTE: Migrated device private page on some
+ *					other device
+ */
+enum {
+	HMM_DMIRROR_PROT_ERROR			= 0xFF,
+	HMM_DMIRROR_PROT_NONE			= 0x00,
+	HMM_DMIRROR_PROT_READ			= 0x01,
+	HMM_DMIRROR_PROT_WRITE			= 0x02,
+	HMM_DMIRROR_PROT_ZERO			= 0x10,
+	HMM_DMIRROR_PROT_DEV_PRIVATE_LOCAL	= 0x20,
+	HMM_DMIRROR_PROT_DEV_PRIVATE_REMOTE	= 0x30,
+};
+
+#endif /* _UAPI_LINUX_HMM_DMIRROR_H */
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 93d97f9b0157..0354379d6cd0 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2057,6 +2057,17 @@  config TEST_MEMINIT
 
 	  If unsure, say N.
 
+config TEST_HMM
+	tristate "Test HMM (Heterogeneous Memory Management)"
+	depends on HMM_MIRROR
+	depends on DEVICE_PRIVATE
+	help
+	  This is a pseudo device driver solely for testing HMM.
+	  Say M here if you want to build the HMM test module.
+	  Doing so will allow you to run tools/testing/selftest/vm/hmm-tests.
+
+	  If unsure, say N.
+
 endif # RUNTIME_TESTING_MENU
 
 config MEMTEST
diff --git a/lib/Makefile b/lib/Makefile
index c5892807e06f..6a9a0e564866 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -89,6 +89,7 @@  obj-$(CONFIG_TEST_OBJAGG) += test_objagg.o
 obj-$(CONFIG_TEST_STACKINIT) += test_stackinit.o
 obj-$(CONFIG_TEST_BLACKHOLE_DEV) += test_blackhole_dev.o
 obj-$(CONFIG_TEST_MEMINIT) += test_meminit.o
+obj-$(CONFIG_TEST_HMM) += test_hmm.o
 
 obj-$(CONFIG_TEST_LIVEPATCH) += livepatch/
 
diff --git a/lib/test_hmm.c b/lib/test_hmm.c
new file mode 100644
index 000000000000..9887a804d75a
--- /dev/null
+++ b/lib/test_hmm.c
@@ -0,0 +1,1306 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * This is a module to test the HMM (Heterogeneous Memory Management)
+ * mirror and zone device private memory migration APIs of the kernel.
+ * Userspace programs can register with the driver to mirror their own address
+ * space and can use the device to read/write any valid virtual address.
+ *
+ * In some ways it can also serve as an example driver for people wanting to use
+ * HMM inside their own device driver.
+ */
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/cdev.h>
+#include <linux/device.h>
+#include <linux/mutex.h>
+#include <linux/rwsem.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/highmem.h>
+#include <linux/delay.h>
+#include <linux/pagemap.h>
+#include <linux/hmm.h>
+#include <linux/vmalloc.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
+#include <linux/sched/mm.h>
+#include <linux/platform_device.h>
+
+#include <uapi/linux/test_hmm.h>
+
+#define DMIRROR_NDEVICES		2
+#define DMIRROR_RANGE_FAULT_TIMEOUT	1000
+#define DEVMEM_CHUNK_SIZE		(256 * 1024 * 1024U)
+#define DEVMEM_CHUNKS_RESERVE		16
+
+static const struct dev_pagemap_ops dmirror_devmem_ops;
+static dev_t dmirror_dev;
+static struct page *dmirror_zero_page;
+
+struct dmirror_device;
+
+struct dmirror_bounce {
+	void			*ptr;
+	unsigned long		size;
+	unsigned long		addr;
+	unsigned long		cpages;
+};
+
+#define DPT_SHIFT PAGE_SHIFT
+#define DPT_VALID (1UL << 0)
+#define DPT_WRITE (1UL << 1)
+#define DPT_DPAGE (1UL << 2)
+
+#define DPT_XA_TAG_WRITE 3UL
+
+static const uint64_t dmirror_hmm_flags[HMM_PFN_FLAG_MAX] = {
+	[HMM_PFN_VALID] = DPT_VALID,
+	[HMM_PFN_WRITE] = DPT_WRITE,
+	[HMM_PFN_DEVICE_PRIVATE] = DPT_DPAGE,
+};
+
+static const uint64_t dmirror_hmm_values[HMM_PFN_VALUE_MAX] = {
+	[HMM_PFN_NONE]    = 0,
+	[HMM_PFN_ERROR]   = 0x10,
+	[HMM_PFN_SPECIAL] = 0x10,
+};
+
+/*
+ * Data attached to the open device file.
+ * Note that it might be shared after a fork().
+ */
+struct dmirror {
+	struct mmu_notifier     notifier;
+	struct dmirror_device	*mdevice;
+	struct xarray		pt;
+	struct mutex		mutex;
+};
+
+struct dmirror_notifier {
+	struct mmu_range_notifier notifier;
+	struct dmirror		*dmirror;
+};
+
+/*
+ * ZONE_DEVICE pages for migration and simulating device memory.
+ */
+struct dmirror_chunk {
+	struct dev_pagemap	pagemap;
+	struct dmirror_device	*mdevice;
+};
+
+/*
+ * Per device data.
+ */
+struct dmirror_device {
+	struct cdev		cdevice;
+	struct hmm_devmem	*devmem;
+
+	unsigned int		devmem_capacity;
+	unsigned int		devmem_count;
+	struct dmirror_chunk	**devmem_chunks;
+	struct mutex		devmem_lock;	/* protects the above */
+
+	unsigned long		calloc;
+	unsigned long		cfree;
+	struct page		*free_pages;
+	spinlock_t		lock;		/* protects the above */
+};
+
+static struct dmirror_device dmirror_devices[DMIRROR_NDEVICES];
+
+static int dmirror_bounce_init(struct dmirror_bounce *bounce,
+			       unsigned long addr,
+			       unsigned long size)
+{
+	bounce->addr = addr;
+	bounce->size = size;
+	bounce->cpages = 0;
+	bounce->ptr = vmalloc(size);
+	if (!bounce->ptr)
+		return -ENOMEM;
+	return 0;
+}
+
+static int dmirror_bounce_copy_from(struct dmirror_bounce *bounce,
+				    unsigned long addr)
+{
+	unsigned long end = addr + bounce->size;
+	char __user *uptr = (void __user *)addr;
+	void *ptr = bounce->ptr;
+
+	for (; addr < end; addr += PAGE_SIZE, ptr += PAGE_SIZE,
+					      uptr += PAGE_SIZE) {
+		int ret;
+
+		ret = copy_from_user(ptr, uptr, PAGE_SIZE);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static int dmirror_bounce_copy_to(struct dmirror_bounce *bounce,
+				  unsigned long addr)
+{
+	unsigned long end = addr + bounce->size;
+	char __user *uptr = (void __user *)addr;
+	void *ptr = bounce->ptr;
+
+	for (; addr < end; addr += PAGE_SIZE, ptr += PAGE_SIZE,
+					      uptr += PAGE_SIZE) {
+		int ret;
+
+		ret = copy_to_user(uptr, ptr, PAGE_SIZE);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static void dmirror_bounce_fini(struct dmirror_bounce *bounce)
+{
+	vfree(bounce->ptr);
+}
+
+static void dmirror_do_update(struct dmirror *dmirror, unsigned long start,
+			      unsigned long end)
+{
+	unsigned long pfn;
+
+	/*
+	 * The XArray doesn't hold references to pages since it relies on
+	 * the mmu notifier to clear pointers when they become stale.
+	 * Therefore, it is OK to just clear the entry.
+	 */
+	for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++)
+		xa_store(&dmirror->pt, pfn, NULL, GFP_KERNEL);
+}
+
+static int dmirror_invalidate_range_start(struct mmu_notifier *mn,
+				const struct mmu_notifier_range *update)
+{
+	struct dmirror *dmirror = container_of(mn, struct dmirror, notifier);
+
+	if (mmu_notifier_range_blockable(update))
+		mutex_lock(&dmirror->mutex);
+	else if (!mutex_trylock(&dmirror->mutex))
+		return -EAGAIN;
+
+	dmirror_do_update(dmirror, update->start, update->end);
+	mutex_unlock(&dmirror->mutex);
+	return 0;
+}
+
+static void dmirror_free_notifier(struct mmu_notifier *mn)
+{
+	struct dmirror *dmirror = container_of(mn, struct dmirror, notifier);
+
+	xa_destroy(&dmirror->pt);
+	kfree(dmirror);
+}
+
+static const struct mmu_notifier_ops dmirror_mn_ops = {
+	.invalidate_range_start = dmirror_invalidate_range_start,
+	.free_notifier = dmirror_free_notifier,
+};
+
+/*
+ * dmirror_new() - allocate and initialize dmirror struct.
+ *
+ * @mdevice: The device this mirror is associated with.
+ * @filp: The active device file descriptor this mirror is associated with.
+ */
+static struct dmirror *dmirror_new(struct dmirror_device *mdevice)
+{
+	struct dmirror *dmirror;
+	int ret;
+
+	/* Mirror this process address space */
+	dmirror = kzalloc(sizeof(*dmirror), GFP_KERNEL);
+	if (dmirror == NULL)
+		goto err;
+
+	dmirror->mdevice = mdevice;
+	mutex_init(&dmirror->mutex);
+	xa_init(&dmirror->pt);
+
+	dmirror->notifier.ops = &dmirror_mn_ops;
+	ret = mmu_notifier_register(&dmirror->notifier, current->mm);
+	if (ret)
+		goto err_free;
+
+	return dmirror;
+
+err_free:
+	kfree(dmirror);
+err:
+	return NULL;
+}
+
+static int dmirror_fops_open(struct inode *inode, struct file *filp)
+{
+	struct cdev *cdev = inode->i_cdev;
+	struct dmirror_device *mdevice;
+	struct dmirror *dmirror;
+
+	/* No exclusive opens. */
+	if (filp->f_flags & O_EXCL)
+		return -EINVAL;
+
+	mdevice = container_of(cdev, struct dmirror_device, cdevice);
+	dmirror = dmirror_new(mdevice);
+	if (!dmirror)
+		return -ENOMEM;
+
+	/* Only the first open registers the address space. */
+	mutex_lock(&mdevice->devmem_lock);
+	if (filp->private_data)
+		goto err_busy;
+	filp->private_data = dmirror;
+	mutex_unlock(&mdevice->devmem_lock);
+
+	return 0;
+
+err_busy:
+	mutex_unlock(&mdevice->devmem_lock);
+	mmu_notifier_put(&dmirror->notifier);
+	return -EBUSY;
+}
+
+static int dmirror_fops_release(struct inode *inode, struct file *filp)
+{
+	struct dmirror *dmirror = filp->private_data;
+
+	if (!dmirror)
+		return 0;
+
+	filp->private_data = NULL;
+	mmu_notifier_put(&dmirror->notifier);
+
+	return 0;
+}
+
+static inline struct dmirror_device *dmirror_page_to_device(struct page *page)
+
+{
+	struct dmirror_chunk *devmem;
+
+	devmem = container_of(page->pgmap, struct dmirror_chunk, pagemap);
+	return devmem->mdevice;
+}
+
+static bool dmirror_device_is_mine(struct dmirror_device *mdevice,
+				   struct page *page)
+{
+	if (!is_zone_device_page(page))
+		return false;
+	return page->pgmap->ops == &dmirror_devmem_ops &&
+		dmirror_page_to_device(page) == mdevice;
+}
+
+static int dmirror_do_fault(struct dmirror *dmirror, unsigned long start,
+			    unsigned long end, struct hmm_range *range)
+{
+	unsigned long idx = (start - range->start) >> PAGE_SHIFT;
+	uint64_t *pfns = range->pfns + idx;
+	unsigned long pfn;
+
+	for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++,
+								   pfns++) {
+		struct page *page;
+		void *entry;
+
+		/*
+		 * HMM_PFN_ERROR is returned if it is accessing invalid memory
+		 * either because of memory error (hardware detected memory
+		 * corruption) or more likely because of truncate on mmap
+		 * file.
+		 */
+		if (*pfns == range->values[HMM_PFN_ERROR])
+			return -EFAULT;
+		if (!(*pfns & range->flags[HMM_PFN_VALID]))
+			return -EFAULT;
+		page = hmm_device_entry_to_page(range, *pfns);
+		/* We asked for pages to be populated but check anyway. */
+		if (!page)
+			return -EFAULT;
+		if (is_zone_device_page(page)) {
+			/*
+			 * TODO: need a way to ask HMM to fault foreign zone
+			 * device private pages.
+			 */
+			if (!dmirror_device_is_mine(dmirror->mdevice, page))
+				continue;
+		}
+		entry = page;
+		if (*pfns & range->flags[HMM_PFN_WRITE])
+			entry = xa_tag_pointer(entry, DPT_XA_TAG_WRITE);
+		else if (range->default_flags & range->flags[HMM_PFN_WRITE])
+			return -EFAULT;
+		entry = xa_store(&dmirror->pt, pfn, entry, GFP_KERNEL);
+		if (xa_is_err(entry))
+			return xa_err(entry);
+	}
+
+	return 0;
+}
+
+static bool dmirror_range_invalidate(struct mmu_range_notifier *mrn,
+				const struct mmu_notifier_range *range,
+				unsigned long cur_seq)
+{
+	struct dmirror_notifier *dn =
+		container_of(mrn, struct dmirror_notifier, notifier);
+
+	/*
+	 * Serializes the update to mrn->invalidate_seq done by caller and
+	 * prevents invalidation from progressing while a device's page table
+	 * is being updated.
+	 */
+	if (mmu_notifier_range_blockable(range))
+		mutex_lock(&dn->dmirror->mutex);
+	else if (!mutex_trylock(&dn->dmirror->mutex))
+		return false;
+	mmu_range_set_seq(mrn, cur_seq);
+	mutex_unlock(&dn->dmirror->mutex);
+	return true;
+}
+
+static const struct mmu_range_notifier_ops dmirror_mrn_ops = {
+	.invalidate = dmirror_range_invalidate,
+};
+
+static int dmirror_range_fault(struct dmirror *dmirror,
+				struct hmm_range *range)
+{
+	struct mm_struct *mm = dmirror->notifier.mm;
+	struct dmirror_notifier notifier;
+	unsigned long timeout =
+		jiffies + msecs_to_jiffies(HMM_RANGE_DEFAULT_TIMEOUT);
+	int ret;
+
+	/* Since the mm is for the mirrored process, get a reference first. */
+	if (!mmget_not_zero(mm))
+		return 0;
+
+	notifier.dmirror = dmirror;
+	notifier.notifier.ops = &dmirror_mrn_ops;
+	range->notifier = &notifier.notifier;
+
+	ret = mmu_range_notifier_insert(&notifier.notifier, range->start,
+					range->end - range->start, mm);
+	if (ret)
+		return ret;
+
+	while (true) {
+		long count;
+
+		if (time_after(jiffies, timeout)) {
+			ret = -EBUSY;
+			goto out;
+		}
+
+		range->notifier_seq = mmu_range_read_begin(range->notifier);
+
+		down_read(&mm->mmap_sem);
+		count = hmm_range_fault(range, 0);
+		up_read(&mm->mmap_sem);
+		if (count <= 0) {
+			if (count == 0 || count == -EBUSY)
+				continue;
+			ret = count;
+			goto out;
+		}
+
+		mutex_lock(&dmirror->mutex);
+		if (mmu_range_read_retry(range->notifier,
+					 range->notifier_seq)) {
+			mutex_unlock(&dmirror->mutex);
+			continue;
+		}
+		break;
+	}
+
+	ret = dmirror_do_fault(dmirror, range->start, range->end, range);
+
+	mutex_unlock(&dmirror->mutex);
+out:
+	mmu_range_notifier_remove(&notifier.notifier);
+	mmput(mm);
+	return ret;
+}
+
+static int dmirror_fault(struct dmirror *dmirror, unsigned long start,
+			 unsigned long end, bool write)
+{
+	struct mm_struct *mm = dmirror->notifier.mm;
+	unsigned long addr;
+	unsigned long next;
+	uint64_t pfns[64];
+	struct hmm_range range = {
+		.pfns = pfns,
+		.flags = dmirror_hmm_flags,
+		.values = dmirror_hmm_values,
+		.pfn_shift = DPT_SHIFT,
+		.pfn_flags_mask = ~(dmirror_hmm_flags[HMM_PFN_VALID] |
+				    dmirror_hmm_flags[HMM_PFN_WRITE]),
+		.default_flags = dmirror_hmm_flags[HMM_PFN_VALID] |
+				(write ? dmirror_hmm_flags[HMM_PFN_WRITE] : 0),
+	};
+	int ret = 0;
+
+	/* Since the mm is for the mirrored process, get a reference first. */
+	if (!mmget_not_zero(mm))
+		return 0;
+
+	for (addr = start; addr < end; addr = next) {
+		next = min(addr + (ARRAY_SIZE(pfns) << PAGE_SHIFT), end);
+		range.start = addr;
+		range.end = next;
+
+		ret = dmirror_range_fault(dmirror, &range);
+		if (ret)
+			break;
+	}
+	mmput(mm);
+
+	return ret;
+}
+
+static int dmirror_do_read(struct dmirror *dmirror, unsigned long start,
+			   unsigned long end, struct dmirror_bounce *bounce)
+{
+	unsigned long pfn;
+	void *ptr;
+
+	ptr = bounce->ptr + ((start - bounce->addr) & PAGE_MASK);
+
+	for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++) {
+		void *entry;
+		struct page *page;
+		void *tmp;
+
+		entry = xa_load(&dmirror->pt, pfn);
+		page = xa_untag_pointer(entry);
+		if (!page)
+			return -ENOENT;
+
+		tmp = kmap(page);
+		memcpy(ptr, tmp, PAGE_SIZE);
+		kunmap(page);
+
+		ptr += PAGE_SIZE;
+		bounce->cpages++;
+	}
+
+	return 0;
+}
+
+static int dmirror_read(struct dmirror *dmirror, struct hmm_dmirror_cmd *cmd)
+{
+	struct dmirror_bounce bounce;
+	unsigned long start, end;
+	unsigned long size = cmd->npages << PAGE_SHIFT;
+	int ret;
+
+	start = cmd->addr;
+	end = start + size;
+	if (end < start)
+		return -EINVAL;
+
+	ret = dmirror_bounce_init(&bounce, start, size);
+	if (ret)
+		return ret;
+
+again:
+	mutex_lock(&dmirror->mutex);
+	ret = dmirror_do_read(dmirror, start, end, &bounce);
+	mutex_unlock(&dmirror->mutex);
+	if (ret == 0)
+		ret = dmirror_bounce_copy_to(&bounce, cmd->ptr);
+	else if (ret == -ENOENT) {
+		start = cmd->addr + (bounce.cpages << PAGE_SHIFT);
+		ret = dmirror_fault(dmirror, start, end, false);
+		if (ret == 0) {
+			cmd->faults++;
+			goto again;
+		}
+	}
+
+	cmd->cpages = bounce.cpages;
+	dmirror_bounce_fini(&bounce);
+	return ret;
+}
+
+static int dmirror_do_write(struct dmirror *dmirror, unsigned long start,
+			    unsigned long end, struct dmirror_bounce *bounce)
+{
+	unsigned long pfn;
+	void *ptr;
+
+	ptr = bounce->ptr + ((start - bounce->addr) & PAGE_MASK);
+
+	for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++) {
+		void *entry;
+		struct page *page;
+		void *tmp;
+
+		entry = xa_load(&dmirror->pt, pfn);
+		page = xa_untag_pointer(entry);
+		if (!page || xa_pointer_tag(entry) != DPT_XA_TAG_WRITE)
+			return -ENOENT;
+
+		tmp = kmap(page);
+		memcpy(tmp, ptr, PAGE_SIZE);
+		kunmap(page);
+
+		ptr += PAGE_SIZE;
+		bounce->cpages++;
+	}
+
+	return 0;
+}
+
+static int dmirror_write(struct dmirror *dmirror, struct hmm_dmirror_cmd *cmd)
+{
+	struct dmirror_bounce bounce;
+	unsigned long start, end;
+	unsigned long size = cmd->npages << PAGE_SHIFT;
+	int ret;
+
+	start = cmd->addr;
+	end = start + size;
+	if (end < start)
+		return -EINVAL;
+
+	ret = dmirror_bounce_init(&bounce, start, size);
+	if (ret)
+		return ret;
+	ret = dmirror_bounce_copy_from(&bounce, cmd->ptr);
+	if (ret)
+		return ret;
+
+again:
+	mutex_lock(&dmirror->mutex);
+	ret = dmirror_do_write(dmirror, start, end, &bounce);
+	mutex_unlock(&dmirror->mutex);
+	if (ret == -ENOENT) {
+		start = cmd->addr + (bounce.cpages << PAGE_SHIFT);
+		ret = dmirror_fault(dmirror, start, end, true);
+		if (ret == 0) {
+			cmd->faults++;
+			goto again;
+		}
+	}
+
+	cmd->cpages = bounce.cpages;
+	dmirror_bounce_fini(&bounce);
+	return ret;
+}
+
+static bool dmirror_allocate_chunk(struct dmirror_device *mdevice,
+				   struct page **ppage)
+{
+	struct dmirror_chunk *devmem;
+	struct resource *res;
+	unsigned long pfn;
+	unsigned long pfn_first;
+	unsigned long pfn_last;
+	void *ptr;
+
+	mutex_lock(&mdevice->devmem_lock);
+
+	if (mdevice->devmem_count == mdevice->devmem_capacity) {
+		struct dmirror_chunk **new_chunks;
+		unsigned int new_capacity;
+
+		new_capacity = mdevice->devmem_capacity +
+				DEVMEM_CHUNKS_RESERVE;
+		new_chunks = krealloc(mdevice->devmem_chunks,
+				sizeof(new_chunks[0]) * new_capacity,
+				GFP_KERNEL);
+		if (!new_chunks)
+			goto err;
+		mdevice->devmem_capacity = new_capacity;
+		mdevice->devmem_chunks = new_chunks;
+	}
+
+	res = request_free_mem_region(&iomem_resource, DEVMEM_CHUNK_SIZE,
+					"hmm_dmirror");
+	if (IS_ERR(res))
+		goto err;
+
+	devmem = kzalloc(sizeof(*devmem), GFP_KERNEL);
+	if (!devmem)
+		goto err;
+
+	devmem->pagemap.type = MEMORY_DEVICE_PRIVATE;
+	devmem->pagemap.res = *res;
+	devmem->pagemap.ops = &dmirror_devmem_ops;
+
+	/* Numa node ID doesn't matter for ZONE_DEVICE private pages. */
+	ptr = memremap_pages(&devmem->pagemap, 0);
+	if (IS_ERR(ptr))
+		goto err_free;
+
+	devmem->mdevice = mdevice;
+	pfn_first = devmem->pagemap.res.start >> PAGE_SHIFT;
+	pfn_last = pfn_first +
+		(resource_size(&devmem->pagemap.res) >> PAGE_SHIFT);
+	mdevice->devmem_chunks[mdevice->devmem_count++] = devmem;
+
+	mutex_unlock(&mdevice->devmem_lock);
+
+	pr_info("added new %u MB chunk (total %u chunks, %u MB) PFNs [0x%lx 0x%lx)\n",
+		DEVMEM_CHUNK_SIZE / (1024 * 1024),
+		mdevice->devmem_count,
+		mdevice->devmem_count * (DEVMEM_CHUNK_SIZE / (1024 * 1024)),
+		pfn_first, pfn_last);
+
+	spin_lock(&mdevice->lock);
+	for (pfn = pfn_first; pfn < pfn_last; pfn++) {
+		struct page *page = pfn_to_page(pfn);
+
+		page->zone_device_data = mdevice->free_pages;
+		mdevice->free_pages = page;
+	}
+	if (ppage) {
+		*ppage = mdevice->free_pages;
+		mdevice->free_pages = (*ppage)->zone_device_data;
+		mdevice->calloc++;
+	}
+	spin_unlock(&mdevice->lock);
+
+	return true;
+
+err_free:
+	kfree(devmem);
+err:
+	mutex_unlock(&mdevice->devmem_lock);
+	return false;
+}
+
+static struct page *dmirror_devmem_alloc_page(struct dmirror_device *mdevice)
+{
+	struct page *dpage = NULL;
+	struct page *rpage;
+
+	/*
+	 * This is a fake device so we alloc real system memory to store
+	 * our device memory.
+	 */
+	rpage = alloc_page(GFP_HIGHUSER);
+	if (!rpage)
+		return NULL;
+
+	spin_lock(&mdevice->lock);
+
+	if (mdevice->free_pages) {
+		dpage = mdevice->free_pages;
+		mdevice->free_pages = dpage->zone_device_data;
+		mdevice->calloc++;
+		spin_unlock(&mdevice->lock);
+	} else {
+		spin_unlock(&mdevice->lock);
+		if (!dmirror_allocate_chunk(mdevice, &dpage))
+			goto error;
+	}
+
+	dpage->zone_device_data = rpage;
+	get_page(dpage);
+	lock_page(dpage);
+	return dpage;
+
+error:
+	__free_page(rpage);
+	return NULL;
+}
+
+static void dmirror_migrate_alloc_and_copy(struct migrate_vma *args,
+					   struct dmirror *dmirror)
+{
+	struct dmirror_device *mdevice = dmirror->mdevice;
+	const unsigned long *src = args->src;
+	unsigned long *dst = args->dst;
+	unsigned long addr;
+
+	for (addr = args->start; addr < args->end; addr += PAGE_SIZE,
+						   src++, dst++) {
+		struct page *spage;
+		struct page *dpage;
+		struct page *rpage;
+
+		if (!(*src & MIGRATE_PFN_MIGRATE))
+			continue;
+
+		/*
+		 * Note that spage might be NULL which is OK since it is an
+		 * unallocated pte_none() or read-only zero page.
+		 */
+		spage = migrate_pfn_to_page(*src);
+
+		/*
+		 * Don't migrate device private pages from our own driver or
+		 * others. For our own we would do a device private memory copy
+		 * not a migration and for others, we would need to fault the
+		 * other device's page into system memory first.
+		 */
+		if (spage && is_zone_device_page(spage))
+			continue;
+
+		dpage = dmirror_devmem_alloc_page(mdevice);
+		if (!dpage)
+			continue;
+
+		rpage = dpage->zone_device_data;
+		if (spage)
+			copy_highpage(rpage, spage);
+		else
+			clear_highpage(rpage);
+
+		/*
+		 * Normally, a device would use the page->zone_device_data to
+		 * point to the mirror but here we use it to hold the page for
+		 * the simulated device memory and that page holds the pointer
+		 * to the mirror.
+		 */
+		rpage->zone_device_data = dmirror;
+
+		*dst = migrate_pfn(page_to_pfn(dpage)) |
+			    MIGRATE_PFN_LOCKED;
+		if ((*src & MIGRATE_PFN_WRITE) ||
+		    (!spage && args->vma->vm_flags & VM_WRITE))
+			*dst |= MIGRATE_PFN_WRITE;
+	}
+}
+
+struct dmirror_migrate {
+	struct hmm_dmirror_cmd		*cmd;
+	const unsigned long		*src;
+	const unsigned long		*dst;
+	unsigned long			start;
+};
+
+static int dmirror_do_migrate(struct dmirror *dmirror, unsigned long start,
+			      unsigned long end,
+			      struct dmirror_migrate *migrate)
+{
+	unsigned long idx = (start - migrate->start) >> PAGE_SHIFT;
+	const unsigned long *src = migrate->src + idx;
+	const unsigned long *dst = migrate->dst + idx;
+	unsigned long pfn;
+
+	for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++,
+								src++, dst++) {
+		struct page *page;
+		void *entry;
+
+		if (!(*src & MIGRATE_PFN_MIGRATE))
+			continue;
+
+		page = migrate_pfn_to_page(*dst);
+		if (!page)
+			continue;
+
+		/*
+		 * Store the page that holds the data so the page table
+		 * doesn't have to deal with ZONE_DEVICE private pages.
+		 */
+		entry = page->zone_device_data;
+		if (*dst & MIGRATE_PFN_WRITE)
+			entry = xa_tag_pointer(entry, DPT_XA_TAG_WRITE);
+		entry = xa_store(&dmirror->pt, pfn, entry, GFP_KERNEL);
+		if (xa_is_err(entry))
+			return xa_err(entry);
+	}
+
+	return 0;
+}
+
+static void dmirror_migrate_finalize_and_map(struct migrate_vma *args,
+					     struct dmirror *dmirror,
+					     struct hmm_dmirror_cmd *cmd)
+{
+	struct dmirror_migrate migrate;
+
+	migrate.cmd = cmd;
+	migrate.src = args->src;
+	migrate.dst = args->dst;
+	migrate.start = args->start;
+
+	/* Map the migrated pages into the device's page tables. */
+	mutex_lock(&dmirror->mutex);
+	dmirror_do_migrate(dmirror, args->start, args->end, &migrate);
+	mutex_unlock(&dmirror->mutex);
+}
+
+static int dmirror_migrate(struct dmirror *dmirror,
+			   struct hmm_dmirror_cmd *cmd)
+{
+	unsigned long start, end, addr;
+	unsigned long size = cmd->npages << PAGE_SHIFT;
+	struct mm_struct *mm = dmirror->notifier.mm;
+	struct vm_area_struct *vma;
+	unsigned long src_pfns[64];
+	unsigned long dst_pfns[64];
+	struct dmirror_bounce bounce;
+	struct migrate_vma args;
+	unsigned long next;
+	int ret;
+
+	start = cmd->addr;
+	end = start + size;
+	if (end < start)
+		return -EINVAL;
+
+	/* Since the mm is for the mirrored process, get a reference first. */
+	if (!mmget_not_zero(mm))
+		return -EINVAL;
+
+	down_read(&mm->mmap_sem);
+	for (addr = start; addr < end; addr = next) {
+		vma = find_vma(mm, addr);
+		if (!vma || addr < vma->vm_start) {
+			ret = -EINVAL;
+			goto out;
+		}
+		next = min(end, addr + (ARRAY_SIZE(src_pfns) << PAGE_SHIFT));
+		if (next > vma->vm_end)
+			next = vma->vm_end;
+
+		args.vma = vma;
+		args.src = src_pfns;
+		args.dst = dst_pfns;
+		args.start = addr;
+		args.end = next;
+		ret = migrate_vma_setup(&args);
+		if (ret)
+			goto out;
+
+		dmirror_migrate_alloc_and_copy(&args, dmirror);
+		migrate_vma_pages(&args);
+		dmirror_migrate_finalize_and_map(&args, dmirror, cmd);
+		migrate_vma_finalize(&args);
+	}
+	up_read(&mm->mmap_sem);
+	mmput(mm);
+
+	/* Return the migrated data for verification. */
+	ret = dmirror_bounce_init(&bounce, start, size);
+	if (ret)
+		return ret;
+	mutex_lock(&dmirror->mutex);
+	ret = dmirror_do_read(dmirror, start, end, &bounce);
+	mutex_unlock(&dmirror->mutex);
+	if (ret == 0)
+		ret = dmirror_bounce_copy_to(&bounce, cmd->ptr);
+	cmd->cpages = bounce.cpages;
+	dmirror_bounce_fini(&bounce);
+	return ret;
+
+out:
+	up_read(&mm->mmap_sem);
+	return ret;
+}
+
+static void dmirror_mkentry(struct dmirror *dmirror, struct hmm_range *range,
+			    unsigned char *perm, uint64_t entry)
+{
+	struct page *page;
+
+	if (entry == range->values[HMM_PFN_ERROR]) {
+		*perm = HMM_DMIRROR_PROT_ERROR;
+		return;
+	}
+	page = hmm_device_entry_to_page(range, entry);
+	if (!page) {
+		*perm = HMM_DMIRROR_PROT_NONE;
+		return;
+	}
+	if (entry & range->flags[HMM_PFN_DEVICE_PRIVATE]) {
+		/* Is the page migrated to this device or some other? */
+		if (dmirror->mdevice == dmirror_page_to_device(page))
+			*perm = HMM_DMIRROR_PROT_DEV_PRIVATE_LOCAL;
+		else
+			*perm = HMM_DMIRROR_PROT_DEV_PRIVATE_REMOTE;
+	} else if (is_zero_pfn(page_to_pfn(page)))
+		*perm = HMM_DMIRROR_PROT_ZERO;
+	else
+		*perm = HMM_DMIRROR_PROT_NONE;
+	if (entry & range->flags[HMM_PFN_WRITE])
+		*perm |= HMM_DMIRROR_PROT_WRITE;
+	else
+		*perm |= HMM_DMIRROR_PROT_READ;
+}
+
+static int dmirror_range_snapshot(struct dmirror *dmirror,
+				  struct hmm_range *range,
+				  unsigned char *perm)
+{
+	struct mm_struct *mm = dmirror->notifier.mm;
+	struct dmirror_notifier notifier;
+	unsigned long timeout =
+		jiffies + msecs_to_jiffies(HMM_RANGE_DEFAULT_TIMEOUT);
+	unsigned long i;
+	unsigned long n;
+	int ret;
+
+	/* Since the mm is for the mirrored process, get a reference first. */
+	if (!mmget_not_zero(mm))
+		return 0;
+
+	notifier.dmirror = dmirror;
+	notifier.notifier.ops = &dmirror_mrn_ops;
+	range->notifier = &notifier.notifier;
+
+	ret = mmu_range_notifier_insert(&notifier.notifier, range->start,
+					range->end - range->start, mm);
+	if (ret)
+		return ret;
+
+	while (true) {
+		long count;
+
+		if (time_after(jiffies, timeout)) {
+			ret = -EBUSY;
+			goto out;
+		}
+
+		range->notifier_seq = mmu_range_read_begin(range->notifier);
+		down_read(&mm->mmap_sem);
+		count = hmm_range_fault(range, HMM_FAULT_SNAPSHOT);
+		up_read(&mm->mmap_sem);
+		if (count <= 0) {
+			if (count == 0 || count == -EBUSY)
+				continue;
+			ret = count;
+			goto out;
+		}
+
+		mutex_lock(&dmirror->mutex);
+		if (mmu_range_read_retry(range->notifier,
+					 range->notifier_seq)) {
+			mutex_unlock(&dmirror->mutex);
+			continue;
+		}
+		break;
+	}
+
+	n = (range->end - range->start) >> PAGE_SHIFT;
+	for (i = 0; i < n; i++)
+		dmirror_mkentry(dmirror, range, perm + i, range->pfns[i]);
+
+	mutex_unlock(&dmirror->mutex);
+out:
+	mmu_range_notifier_remove(&notifier.notifier);
+	mmput(mm);
+	return ret;
+}
+
+static int dmirror_snapshot(struct dmirror *dmirror,
+			    struct hmm_dmirror_cmd *cmd)
+{
+	struct mm_struct *mm = dmirror->notifier.mm;
+	unsigned long start, end;
+	unsigned long size = cmd->npages << PAGE_SHIFT;
+	unsigned long addr;
+	unsigned long next;
+	uint64_t pfns[64];
+	unsigned char perm[64];
+	char __user *uptr;
+	struct hmm_range range = {
+		.pfns = pfns,
+		.flags = dmirror_hmm_flags,
+		.values = dmirror_hmm_values,
+		.pfn_shift = DPT_SHIFT,
+		.pfn_flags_mask = ~0ULL,
+	};
+	int ret = 0;
+
+	start = cmd->addr;
+	end = start + size;
+	uptr = (void __user *)cmd->ptr;
+
+	/* Since the mm is for the mirrored process, get a reference first. */
+	if (!mmget_not_zero(mm))
+		return -EINVAL;
+
+	for (addr = start; addr < end; addr = next) {
+		unsigned long n;
+
+		next = min(addr + (ARRAY_SIZE(pfns) << PAGE_SHIFT), end);
+		range.start = addr;
+		range.end = next;
+
+		ret = dmirror_range_snapshot(dmirror, &range, perm);
+		if (ret)
+			break;
+
+		n = (range.end - range.start) >> PAGE_SHIFT;
+		ret = copy_to_user(uptr, perm, n);
+		if (ret)
+			break;
+
+		cmd->cpages += n;
+		uptr += n;
+	}
+	mmput(mm);
+
+	return ret;
+}
+
+static long dmirror_fops_unlocked_ioctl(struct file *filp,
+					unsigned int command,
+					unsigned long arg)
+{
+	void __user *uarg = (void __user *)arg;
+	struct hmm_dmirror_cmd cmd;
+	struct dmirror *dmirror;
+	int ret;
+
+	dmirror = filp->private_data;
+	if (!dmirror)
+		return -EINVAL;
+
+	ret = copy_from_user(&cmd, uarg, sizeof(cmd));
+	if (ret)
+		return ret;
+
+	if (cmd.addr & ~PAGE_MASK)
+		return -EINVAL;
+	if (cmd.addr >= (cmd.addr + (cmd.npages << PAGE_SHIFT)))
+		return -EINVAL;
+
+	cmd.cpages = 0;
+	cmd.faults = 0;
+
+	switch (command) {
+	case HMM_DMIRROR_READ:
+		ret = dmirror_read(dmirror, &cmd);
+		break;
+
+	case HMM_DMIRROR_WRITE:
+		ret = dmirror_write(dmirror, &cmd);
+		break;
+
+	case HMM_DMIRROR_MIGRATE:
+		ret = dmirror_migrate(dmirror, &cmd);
+		break;
+
+	case HMM_DMIRROR_SNAPSHOT:
+		ret = dmirror_snapshot(dmirror, &cmd);
+		break;
+
+	default:
+		return -EINVAL;
+	}
+	if (ret)
+		return ret;
+
+	return copy_to_user(uarg, &cmd, sizeof(cmd));
+}
+
+static const struct file_operations dmirror_fops = {
+	.open		= dmirror_fops_open,
+	.release	= dmirror_fops_release,
+	.unlocked_ioctl = dmirror_fops_unlocked_ioctl,
+	.llseek		= default_llseek,
+	.owner		= THIS_MODULE,
+};
+
+static void dmirror_devmem_free(struct page *page)
+{
+	struct page *rpage = page->zone_device_data;
+	struct dmirror_device *mdevice;
+
+	if (rpage)
+		__free_page(rpage);
+
+	mdevice = dmirror_page_to_device(page);
+
+	spin_lock(&mdevice->lock);
+	mdevice->cfree++;
+	page->zone_device_data = mdevice->free_pages;
+	mdevice->free_pages = page;
+	spin_unlock(&mdevice->lock);
+}
+
+static vm_fault_t dmirror_devmem_fault_alloc_and_copy(struct migrate_vma *args,
+						struct dmirror_device *mdevice)
+{
+	struct vm_area_struct *vma = args->vma;
+	const unsigned long *src = args->src;
+	unsigned long *dst = args->dst;
+	unsigned long start = args->start;
+	unsigned long end = args->end;
+	unsigned long addr;
+
+	for (addr = start; addr < end; addr += PAGE_SIZE,
+				       src++, dst++) {
+		struct page *dpage, *spage;
+
+		spage = migrate_pfn_to_page(*src);
+		if (!spage || !(*src & MIGRATE_PFN_MIGRATE))
+			continue;
+		if (!dmirror_device_is_mine(mdevice, spage))
+			continue;
+		spage = spage->zone_device_data;
+
+		dpage = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, addr);
+		if (!dpage)
+			continue;
+
+		lock_page(dpage);
+		copy_highpage(dpage, spage);
+		*dst = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_LOCKED;
+		if (*src & MIGRATE_PFN_WRITE)
+			*dst |= MIGRATE_PFN_WRITE;
+	}
+	return 0;
+}
+
+static void dmirror_devmem_fault_finalize_and_map(struct migrate_vma *args,
+						  struct dmirror *dmirror)
+{
+	/* Invalidate the device's page table mapping. */
+	mutex_lock(&dmirror->mutex);
+	dmirror_do_update(dmirror, args->start, args->end);
+	mutex_unlock(&dmirror->mutex);
+}
+
+static vm_fault_t dmirror_devmem_fault(struct vm_fault *vmf)
+{
+	struct migrate_vma args;
+	unsigned long src_pfns;
+	unsigned long dst_pfns;
+	struct page *rpage;
+	struct dmirror *dmirror;
+	vm_fault_t ret;
+
+	/* FIXME demonstrate how we can adjust migrate range */
+	args.vma = vmf->vma;
+	args.start = vmf->address;
+	args.end = args.start + PAGE_SIZE;
+	args.src = &src_pfns;
+	args.dst = &dst_pfns;
+
+	if (migrate_vma_setup(&args))
+		return VM_FAULT_SIGBUS;
+
+	/*
+	 * Normally, a device would use the page->zone_device_data to point to
+	 * the mirror but here we use it to hold the page for the simulated
+	 * device memory and that page holds the pointer to the mirror.
+	 */
+	rpage = vmf->page->zone_device_data;
+	dmirror = rpage->zone_device_data;
+
+	ret = dmirror_devmem_fault_alloc_and_copy(&args, dmirror->mdevice);
+	if (ret)
+		return ret;
+	migrate_vma_pages(&args);
+	dmirror_devmem_fault_finalize_and_map(&args, dmirror);
+	migrate_vma_finalize(&args);
+	return 0;
+}
+
+static const struct dev_pagemap_ops dmirror_devmem_ops = {
+	.page_free	= dmirror_devmem_free,
+	.migrate_to_ram	= dmirror_devmem_fault,
+};
+
+static int dmirror_device_init(struct dmirror_device *mdevice, int id)
+{
+	dev_t dev;
+	int ret;
+
+	dev = MKDEV(MAJOR(dmirror_dev), id);
+	mutex_init(&mdevice->devmem_lock);
+	spin_lock_init(&mdevice->lock);
+
+	cdev_init(&mdevice->cdevice, &dmirror_fops);
+	ret = cdev_add(&mdevice->cdevice, dev, 1);
+	if (ret)
+		return ret;
+
+	/* Build a list of free ZONE_DEVICE private struct pages */
+	dmirror_allocate_chunk(mdevice, NULL);
+
+	return 0;
+}
+
+static void dmirror_device_remove(struct dmirror_device *mdevice)
+{
+	unsigned int i;
+
+	if (mdevice->devmem_chunks) {
+		for (i = 0; i < mdevice->devmem_count; i++) {
+			struct dmirror_chunk *devmem =
+				mdevice->devmem_chunks[i];
+
+			memunmap_pages(&devmem->pagemap);
+			kfree(devmem);
+		}
+		kfree(mdevice->devmem_chunks);
+	}
+
+	cdev_del(&mdevice->cdevice);
+}
+
+static int __init hmm_dmirror_init(void)
+{
+	int ret;
+	int id;
+
+	ret = alloc_chrdev_region(&dmirror_dev, 0, DMIRROR_NDEVICES,
+				  "HMM_DMIRROR");
+	if (ret)
+		goto err_unreg;
+
+	for (id = 0; id < DMIRROR_NDEVICES; id++) {
+		ret = dmirror_device_init(dmirror_devices + id, id);
+		if (ret)
+			goto err_chrdev;
+	}
+
+	/*
+	 * Allocate a zero page to simulate a reserved page of device private
+	 * memory which is always zero. The zero_pfn page isn't used just to
+	 * make the code here simpler (i.e., we need a struct page for it).
+	 */
+	dmirror_zero_page = alloc_page(GFP_HIGHUSER | __GFP_ZERO);
+	if (!dmirror_zero_page)
+		goto err_chrdev;
+
+	pr_info("HMM test module loaded. This is only for testing HMM.\n");
+	return 0;
+
+err_chrdev:
+	while (--id >= 0)
+		dmirror_device_remove(dmirror_devices + id);
+	unregister_chrdev_region(dmirror_dev, DMIRROR_NDEVICES);
+err_unreg:
+	return ret;
+}
+
+static void __exit hmm_dmirror_exit(void)
+{
+	int id;
+
+	if (dmirror_zero_page)
+		__free_page(dmirror_zero_page);
+	for (id = 0; id < DMIRROR_NDEVICES; id++)
+		dmirror_device_remove(dmirror_devices + id);
+	unregister_chrdev_region(dmirror_dev, DMIRROR_NDEVICES);
+	mmu_notifier_synchronize();
+}
+
+module_init(hmm_dmirror_init);
+module_exit(hmm_dmirror_exit);
+MODULE_LICENSE("GPL");
diff --git a/tools/testing/selftests/vm/.gitignore b/tools/testing/selftests/vm/.gitignore
index 31b3c98b6d34..3054565b3f07 100644
--- a/tools/testing/selftests/vm/.gitignore
+++ b/tools/testing/selftests/vm/.gitignore
@@ -14,3 +14,4 @@  virtual_address_range
 gup_benchmark
 va_128TBswitch
 map_fixed_noreplace
+hmm-tests
diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile
index 9534dc2bc929..5643cfb5e3d6 100644
--- a/tools/testing/selftests/vm/Makefile
+++ b/tools/testing/selftests/vm/Makefile
@@ -5,6 +5,7 @@  CFLAGS = -Wall -I ../../../../usr/include $(EXTRA_CFLAGS)
 LDLIBS = -lrt
 TEST_GEN_FILES = compaction_test
 TEST_GEN_FILES += gup_benchmark
+TEST_GEN_FILES += hmm-tests
 TEST_GEN_FILES += hugepage-mmap
 TEST_GEN_FILES += hugepage-shm
 TEST_GEN_FILES += map_hugetlb
@@ -26,6 +27,8 @@  TEST_FILES := test_vmalloc.sh
 KSFT_KHDR_INSTALL := 1
 include ../lib.mk
 
+$(OUTPUT)/hmm-tests: LDLIBS += -lhugetlbfs -lpthread
+
 $(OUTPUT)/userfaultfd: LDLIBS += -lpthread
 
 $(OUTPUT)/mlock-random-test: LDLIBS += -lcap
diff --git a/tools/testing/selftests/vm/config b/tools/testing/selftests/vm/config
index 1c0d76cb5adf..7fd96113575e 100644
--- a/tools/testing/selftests/vm/config
+++ b/tools/testing/selftests/vm/config
@@ -1,2 +1,4 @@ 
 CONFIG_SYSVIPC=y
 CONFIG_USERFAULTFD=y
+CONFIG_HMM_MIRROR=y
+CONFIG_DEVICE_PRIVATE=y
diff --git a/tools/testing/selftests/vm/hmm-tests.c b/tools/testing/selftests/vm/hmm-tests.c
new file mode 100644
index 000000000000..f1e530353bcd
--- /dev/null
+++ b/tools/testing/selftests/vm/hmm-tests.c
@@ -0,0 +1,1295 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * HMM stands for Heterogeneous Memory Management, it is a helper layer inside
+ * the linux kernel to help device drivers mirror a process address space in
+ * the device. This allows the device to use the same address space which
+ * makes communication and data exchange a lot easier.
+ *
+ * This framework's sole purpose is to exercise various code paths inside
+ * the kernel to make sure that HMM performs as expected and to flush out any
+ * bugs.
+ */
+
+#include "../kselftest_harness.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <unistd.h>
+#include <strings.h>
+#include <time.h>
+#include <pthread.h>
+#include <hugetlbfs.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/mman.h>
+#include <sys/ioctl.h>
+#include <linux/test_hmm.h>
+
+struct hmm_buffer {
+	void		*ptr;
+	void		*mirror;
+	unsigned long	size;
+	int		fd;
+	uint64_t	cpages;
+	uint64_t	faults;
+};
+
+#define TWOMEG		(1 << 21)
+#define HMM_BUFFER_SIZE (1024 << 12)
+#define HMM_PATH_MAX    64
+#define NTIMES		256
+
+#define ALIGN(x, a) (((x) + (a - 1)) & (~((a) - 1)))
+
+FIXTURE(hmm)
+{
+	int		fd;
+	unsigned int	page_size;
+	unsigned int	page_shift;
+};
+
+FIXTURE(hmm2)
+{
+	int		fd0;
+	int		fd1;
+	unsigned int	page_size;
+	unsigned int	page_shift;
+};
+
+static int hmm_open(int unit)
+{
+	char pathname[HMM_PATH_MAX];
+	int fd;
+
+	snprintf(pathname, sizeof(pathname), "/dev/hmm_dmirror%d", unit);
+	fd = open(pathname, O_RDWR, 0);
+	if (fd < 0)
+		fprintf(stderr, "could not open hmm dmirror driver (%s)\n",
+			pathname);
+	return fd;
+}
+
+FIXTURE_SETUP(hmm)
+{
+	self->page_size = sysconf(_SC_PAGE_SIZE);
+	self->page_shift = ffs(self->page_size) - 1;
+
+	self->fd = hmm_open(0);
+	ASSERT_GE(self->fd, 0);
+}
+
+FIXTURE_SETUP(hmm2)
+{
+	self->page_size = sysconf(_SC_PAGE_SIZE);
+	self->page_shift = ffs(self->page_size) - 1;
+
+	self->fd0 = hmm_open(0);
+	ASSERT_GE(self->fd0, 0);
+	self->fd1 = hmm_open(1);
+	ASSERT_GE(self->fd1, 0);
+}
+
+FIXTURE_TEARDOWN(hmm)
+{
+	int ret = close(self->fd);
+
+	ASSERT_EQ(ret, 0);
+	self->fd = -1;
+}
+
+FIXTURE_TEARDOWN(hmm2)
+{
+	int ret = close(self->fd0);
+
+	ASSERT_EQ(ret, 0);
+	self->fd0 = -1;
+
+	ret = close(self->fd1);
+	ASSERT_EQ(ret, 0);
+	self->fd1 = -1;
+}
+
+static int hmm_dmirror_cmd(int fd,
+			   unsigned long request,
+			   struct hmm_buffer *buffer,
+			   unsigned long npages)
+{
+	struct hmm_dmirror_cmd cmd;
+	int ret;
+
+	/* Simulate a device reading system memory. */
+	cmd.addr = (__u64)buffer->ptr;
+	cmd.ptr = (__u64)buffer->mirror;
+	cmd.npages = npages;
+
+	for (;;) {
+		ret = ioctl(fd, request, &cmd);
+		if (ret == 0)
+			break;
+		if (errno == EINTR)
+			continue;
+		return -errno;
+	}
+	buffer->cpages = cmd.cpages;
+	buffer->faults = cmd.faults;
+
+	return 0;
+}
+
+static void hmm_buffer_free(struct hmm_buffer *buffer)
+{
+	if (buffer == NULL)
+		return;
+
+	if (buffer->ptr)
+		munmap(buffer->ptr, buffer->size);
+	free(buffer->mirror);
+	free(buffer);
+}
+
+/*
+ * Create a temporary file that will be deleted on close.
+ */
+static int hmm_create_file(unsigned long size)
+{
+	char path[HMM_PATH_MAX];
+	int fd;
+
+	strcpy(path, "/tmp");
+	fd = open(path, O_TMPFILE | O_EXCL | O_RDWR, 0600);
+	if (fd >= 0) {
+		int r;
+
+		do {
+			r = ftruncate(fd, size);
+		} while (r == -1 && errno == EINTR);
+		if (!r)
+			return fd;
+		close(fd);
+	}
+	return -1;
+}
+
+/*
+ * Return a random unsigned number.
+ */
+static unsigned int hmm_random(void)
+{
+	static int fd = -1;
+	unsigned int r;
+
+	if (fd < 0) {
+		fd = open("/dev/urandom", O_RDONLY);
+		if (fd < 0) {
+			fprintf(stderr, "%s:%d failed to open /dev/urandom\n",
+					__FILE__, __LINE__);
+			return ~0U;
+		}
+	}
+	read(fd, &r, sizeof(r));
+	return r;
+}
+
+static void hmm_nanosleep(unsigned int n)
+{
+	struct timespec t;
+
+	t.tv_sec = 0;
+	t.tv_nsec = n;
+	nanosleep(&t, NULL);
+}
+
+/*
+ * Simple NULL test of device open/close.
+ */
+TEST_F(hmm, open_close)
+{
+}
+
+/*
+ * Read private anonymous memory.
+ */
+TEST_F(hmm, anon_read)
+{
+	struct hmm_buffer *buffer;
+	unsigned long npages;
+	unsigned long size;
+	unsigned long i;
+	int *ptr;
+	int ret;
+	int val;
+
+	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
+	ASSERT_NE(npages, 0);
+	size = npages << self->page_shift;
+
+	buffer = malloc(sizeof(*buffer));
+	ASSERT_NE(buffer, NULL);
+
+	buffer->fd = -1;
+	buffer->size = size;
+	buffer->mirror = malloc(size);
+	ASSERT_NE(buffer->mirror, NULL);
+
+	buffer->ptr = mmap(NULL, size,
+			   PROT_READ | PROT_WRITE,
+			   MAP_PRIVATE | MAP_ANONYMOUS,
+			   buffer->fd, 0);
+	ASSERT_NE(buffer->ptr, MAP_FAILED);
+
+	/*
+	 * Initialize buffer in system memory but leave the first two pages
+	 * zero (pte_none and pfn_zero).
+	 */
+	i = 2 * self->page_size / sizeof(*ptr);
+	for (ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ptr[i] = i;
+
+	/* Set buffer permission to read-only. */
+	ret = mprotect(buffer->ptr, size, PROT_READ);
+	ASSERT_EQ(ret, 0);
+
+	/* Populate the CPU page table with a special zero page. */
+	val = *(int *)(buffer->ptr + self->page_size);
+	ASSERT_EQ(val, 0);
+
+	/* Simulate a device reading system memory. */
+	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_READ, buffer, npages);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(buffer->cpages, npages);
+	ASSERT_EQ(buffer->faults, 1);
+
+	/* Check what the device read. */
+	ptr = buffer->mirror;
+	for (i = 0; i < 2 * self->page_size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], 0);
+	for (; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], i);
+
+	hmm_buffer_free(buffer);
+}
+
+/*
+ * Read private anonymous memory which has been protected with
+ * mprotect() PROT_NONE.
+ */
+TEST_F(hmm, anon_read_prot)
+{
+	struct hmm_buffer *buffer;
+	unsigned long npages;
+	unsigned long size;
+	unsigned long i;
+	int *ptr;
+	int ret;
+
+	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
+	ASSERT_NE(npages, 0);
+	size = npages << self->page_shift;
+
+	buffer = malloc(sizeof(*buffer));
+	ASSERT_NE(buffer, NULL);
+
+	buffer->fd = -1;
+	buffer->size = size;
+	buffer->mirror = malloc(size);
+	ASSERT_NE(buffer->mirror, NULL);
+
+	buffer->ptr = mmap(NULL, size,
+			   PROT_READ | PROT_WRITE,
+			   MAP_PRIVATE | MAP_ANONYMOUS,
+			   buffer->fd, 0);
+	ASSERT_NE(buffer->ptr, MAP_FAILED);
+
+	/* Initialize buffer in system memory. */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ptr[i] = i;
+
+	/* Initialize mirror buffer so we can verify it isn't written. */
+	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+		ptr[i] = -i;
+
+	/* Protect buffer from reading. */
+	ret = mprotect(buffer->ptr, size, PROT_NONE);
+	ASSERT_EQ(ret, 0);
+
+	/* Simulate a device reading system memory. */
+	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_READ, buffer, npages);
+	ASSERT_EQ(ret, -EFAULT);
+
+	/* Allow CPU to read the buffer so we can check it. */
+	ret = mprotect(buffer->ptr, size, PROT_READ);
+	ASSERT_EQ(ret, 0);
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], i);
+
+	/* Check what the device read. */
+	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], -i);
+
+	hmm_buffer_free(buffer);
+}
+
+/*
+ * Write private anonymous memory.
+ */
+TEST_F(hmm, anon_write)
+{
+	struct hmm_buffer *buffer;
+	unsigned long npages;
+	unsigned long size;
+	unsigned long i;
+	int *ptr;
+	int ret;
+
+	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
+	ASSERT_NE(npages, 0);
+	size = npages << self->page_shift;
+
+	buffer = malloc(sizeof(*buffer));
+	ASSERT_NE(buffer, NULL);
+
+	buffer->fd = -1;
+	buffer->size = size;
+	buffer->mirror = malloc(size);
+	ASSERT_NE(buffer->mirror, NULL);
+
+	buffer->ptr = mmap(NULL, size,
+			   PROT_READ | PROT_WRITE,
+			   MAP_PRIVATE | MAP_ANONYMOUS,
+			   buffer->fd, 0);
+	ASSERT_NE(buffer->ptr, MAP_FAILED);
+
+	/* Initialize data that the device will write to buffer->ptr. */
+	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+		ptr[i] = i;
+
+	/* Simulate a device writing system memory. */
+	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_WRITE, buffer, npages);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(buffer->cpages, npages);
+	ASSERT_EQ(buffer->faults, 1);
+
+	/* Check what the device wrote. */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], i);
+
+	hmm_buffer_free(buffer);
+}
+
+/*
+ * Write private anonymous memory which has been protected with
+ * mprotect() PROT_READ.
+ */
+TEST_F(hmm, anon_write_prot)
+{
+	struct hmm_buffer *buffer;
+	unsigned long npages;
+	unsigned long size;
+	unsigned long i;
+	int *ptr;
+	int ret;
+
+	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
+	ASSERT_NE(npages, 0);
+	size = npages << self->page_shift;
+
+	buffer = malloc(sizeof(*buffer));
+	ASSERT_NE(buffer, NULL);
+
+	buffer->fd = -1;
+	buffer->size = size;
+	buffer->mirror = malloc(size);
+	ASSERT_NE(buffer->mirror, NULL);
+
+	buffer->ptr = mmap(NULL, size,
+			   PROT_READ,
+			   MAP_PRIVATE | MAP_ANONYMOUS,
+			   buffer->fd, 0);
+	ASSERT_NE(buffer->ptr, MAP_FAILED);
+
+	/* Simulate a device reading a zero page of memory. */
+	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_READ, buffer, 1);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(buffer->cpages, 1);
+	ASSERT_EQ(buffer->faults, 1);
+
+	/* Initialize data that the device will write to buffer->ptr. */
+	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+		ptr[i] = i;
+
+	/* Simulate a device writing system memory. */
+	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_WRITE, buffer, npages);
+	ASSERT_EQ(ret, -EPERM);
+
+	/* Check what the device wrote. */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], 0);
+
+	/* Now allow writing and see that the zero page is replaced. */
+	ret = mprotect(buffer->ptr, size, PROT_WRITE | PROT_READ);
+	ASSERT_EQ(ret, 0);
+
+	/* Simulate a device writing system memory. */
+	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_WRITE, buffer, npages);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(buffer->cpages, npages);
+	ASSERT_EQ(buffer->faults, 1);
+
+	/* Check what the device wrote. */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], i);
+
+	hmm_buffer_free(buffer);
+}
+
+/*
+ * Check that a device writing an anonymous private mapping
+ * will copy-on-write if a child process inherits the mapping.
+ */
+TEST_F(hmm, anon_write_child)
+{
+	struct hmm_buffer *buffer;
+	unsigned long npages;
+	unsigned long size;
+	unsigned long i;
+	int *ptr;
+	pid_t pid;
+	int child_fd;
+	int ret;
+
+	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
+	ASSERT_NE(npages, 0);
+	size = npages << self->page_shift;
+
+	buffer = malloc(sizeof(*buffer));
+	ASSERT_NE(buffer, NULL);
+
+	buffer->fd = -1;
+	buffer->size = size;
+	buffer->mirror = malloc(size);
+	ASSERT_NE(buffer->mirror, NULL);
+
+	buffer->ptr = mmap(NULL, size,
+			   PROT_READ | PROT_WRITE,
+			   MAP_PRIVATE | MAP_ANONYMOUS,
+			   buffer->fd, 0);
+	ASSERT_NE(buffer->ptr, MAP_FAILED);
+
+	/* Initialize buffer->ptr so we can tell if it is written. */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ptr[i] = i;
+
+	/* Initialize data that the device will write to buffer->ptr. */
+	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+		ptr[i] = -i;
+
+	pid = fork();
+	if (pid == -1)
+		ASSERT_EQ(pid, 0);
+	if (pid != 0) {
+		waitpid(pid, &ret, 0);
+		ASSERT_EQ(WIFEXITED(ret), 1);
+
+		/* Check that the parent's buffer did not change. */
+		for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+			ASSERT_EQ(ptr[i], i);
+		return;
+	}
+
+	/* Check that we see the parent's values. */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], i);
+	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], -i);
+
+	/* The child process needs its own mirror to its own mm. */
+	child_fd = hmm_open(0);
+	ASSERT_GE(child_fd, 0);
+
+	/* Simulate a device writing system memory. */
+	ret = hmm_dmirror_cmd(child_fd, HMM_DMIRROR_WRITE, buffer, npages);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(buffer->cpages, npages);
+	ASSERT_EQ(buffer->faults, 1);
+
+	/* Check what the device wrote. */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], -i);
+
+	close(child_fd);
+	exit(0);
+}
+
+/*
+ * Check that a device writing an anonymous shared mapping
+ * will not copy-on-write if a child process inherits the mapping.
+ */
+TEST_F(hmm, anon_write_child_shared)
+{
+	struct hmm_buffer *buffer;
+	unsigned long npages;
+	unsigned long size;
+	unsigned long i;
+	int *ptr;
+	pid_t pid;
+	int child_fd;
+	int ret;
+
+	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
+	ASSERT_NE(npages, 0);
+	size = npages << self->page_shift;
+
+	buffer = malloc(sizeof(*buffer));
+	ASSERT_NE(buffer, NULL);
+
+	buffer->fd = -1;
+	buffer->size = size;
+	buffer->mirror = malloc(size);
+	ASSERT_NE(buffer->mirror, NULL);
+
+	buffer->ptr = mmap(NULL, size,
+			   PROT_READ | PROT_WRITE,
+			   MAP_SHARED | MAP_ANONYMOUS,
+			   buffer->fd, 0);
+	ASSERT_NE(buffer->ptr, MAP_FAILED);
+
+	/* Initialize buffer->ptr so we can tell if it is written. */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ptr[i] = i;
+
+	/* Initialize data that the device will write to buffer->ptr. */
+	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+		ptr[i] = -i;
+
+	pid = fork();
+	if (pid == -1)
+		ASSERT_EQ(pid, 0);
+	if (pid != 0) {
+		waitpid(pid, &ret, 0);
+		ASSERT_EQ(WIFEXITED(ret), 1);
+
+		/* Check that the parent's buffer did change. */
+		for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+			ASSERT_EQ(ptr[i], -i);
+		return;
+	}
+
+	/* Check that we see the parent's values. */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], i);
+	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], -i);
+
+	/* The child process needs its own mirror to its own mm. */
+	child_fd = hmm_open(0);
+	ASSERT_GE(child_fd, 0);
+
+	/* Simulate a device writing system memory. */
+	ret = hmm_dmirror_cmd(child_fd, HMM_DMIRROR_WRITE, buffer, npages);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(buffer->cpages, npages);
+	ASSERT_EQ(buffer->faults, 1);
+
+	/* Check what the device wrote. */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], -i);
+
+	close(child_fd);
+	exit(0);
+}
+
+/*
+ * Write private anonymous huge page.
+ */
+TEST_F(hmm, anon_write_huge)
+{
+	struct hmm_buffer *buffer;
+	unsigned long npages;
+	unsigned long size;
+	unsigned long i;
+	void *old_ptr;
+	void *map;
+	int *ptr;
+	int ret;
+
+	size = 2 * TWOMEG;
+
+	buffer = malloc(sizeof(*buffer));
+	ASSERT_NE(buffer, NULL);
+
+	buffer->fd = -1;
+	buffer->size = size;
+	buffer->mirror = malloc(size);
+	ASSERT_NE(buffer->mirror, NULL);
+
+	buffer->ptr = mmap(NULL, size,
+			   PROT_READ | PROT_WRITE,
+			   MAP_PRIVATE | MAP_ANONYMOUS,
+			   buffer->fd, 0);
+	ASSERT_NE(buffer->ptr, MAP_FAILED);
+
+	size = TWOMEG;
+	npages = size >> self->page_shift;
+	map = (void *)ALIGN((uintptr_t)buffer->ptr, size);
+	ret = madvise(map, size, MADV_HUGEPAGE);
+	ASSERT_EQ(ret, 0);
+	old_ptr = buffer->ptr;
+	buffer->ptr = map;
+
+	/* Initialize data that the device will write to buffer->ptr. */
+	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+		ptr[i] = i;
+
+	/* Simulate a device writing system memory. */
+	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_WRITE, buffer, npages);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(buffer->cpages, npages);
+	ASSERT_EQ(buffer->faults, 1);
+
+	/* Check what the device wrote. */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], i);
+
+	buffer->ptr = old_ptr;
+	hmm_buffer_free(buffer);
+}
+
+/*
+ * Write huge TLBFS page.
+ */
+TEST_F(hmm, anon_write_hugetlbfs)
+{
+	struct hmm_buffer *buffer;
+	unsigned long npages;
+	unsigned long size;
+	unsigned long i;
+	int *ptr;
+	int ret;
+	long pagesizes[4];
+	int n, idx;
+
+	/* Skip test if we can't allocate a hugetlbfs page. */
+
+	n = gethugepagesizes(pagesizes, 4);
+	if (n <= 0)
+		return;
+	for (idx = 0; --n > 0; ) {
+		if (pagesizes[n] < pagesizes[idx])
+			idx = n;
+	}
+	size = ALIGN(TWOMEG, pagesizes[idx]);
+	npages = size >> self->page_shift;
+
+	buffer = malloc(sizeof(*buffer));
+	ASSERT_NE(buffer, NULL);
+
+	buffer->ptr = get_hugepage_region(size, GHR_STRICT);
+	if (buffer->ptr == NULL) {
+		free(buffer);
+		return;
+	}
+
+	buffer->fd = -1;
+	buffer->size = size;
+	buffer->mirror = malloc(size);
+	ASSERT_NE(buffer->mirror, NULL);
+
+	/* Initialize data that the device will write to buffer->ptr. */
+	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+		ptr[i] = i;
+
+	/* Simulate a device writing system memory. */
+	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_WRITE, buffer, npages);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(buffer->cpages, npages);
+	ASSERT_EQ(buffer->faults, 1);
+
+	/* Check what the device wrote. */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], i);
+
+	free_hugepage_region(buffer->ptr);
+	buffer->ptr = NULL;
+	hmm_buffer_free(buffer);
+}
+
+/*
+ * Read mmap'ed file memory.
+ */
+TEST_F(hmm, file_read)
+{
+	struct hmm_buffer *buffer;
+	unsigned long npages;
+	unsigned long size;
+	unsigned long i;
+	int *ptr;
+	int ret;
+	int fd;
+	off_t off;
+	ssize_t len;
+
+	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
+	ASSERT_NE(npages, 0);
+	size = npages << self->page_shift;
+
+	fd = hmm_create_file(size);
+	ASSERT_GE(fd, 0);
+
+	buffer = malloc(sizeof(*buffer));
+	ASSERT_NE(buffer, NULL);
+
+	buffer->fd = fd;
+	buffer->size = size;
+	buffer->mirror = malloc(size);
+	ASSERT_NE(buffer->mirror, NULL);
+
+	/* Write initial contents of the file. */
+	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+		ptr[i] = i;
+	off = lseek(fd, 0, SEEK_SET);
+	ASSERT_EQ(off, 0);
+	len = write(fd, buffer->mirror, size);
+	ASSERT_EQ(len, size);
+	memset(buffer->mirror, 0, size);
+
+	buffer->ptr = mmap(NULL, size,
+			   PROT_READ,
+			   MAP_SHARED,
+			   buffer->fd, 0);
+	ASSERT_NE(buffer->ptr, MAP_FAILED);
+
+	/* Simulate a device reading system memory. */
+	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_READ, buffer, npages);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(buffer->cpages, npages);
+	ASSERT_EQ(buffer->faults, 1);
+
+	/* Check what the device read. */
+	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], i);
+
+	hmm_buffer_free(buffer);
+}
+
+/*
+ * Write mmap'ed file memory.
+ */
+TEST_F(hmm, file_write)
+{
+	struct hmm_buffer *buffer;
+	unsigned long npages;
+	unsigned long size;
+	unsigned long i;
+	int *ptr;
+	int ret;
+	int fd;
+	off_t off;
+	ssize_t len;
+
+	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
+	ASSERT_NE(npages, 0);
+	size = npages << self->page_shift;
+
+	fd = hmm_create_file(size);
+	ASSERT_GE(fd, 0);
+
+	buffer = malloc(sizeof(*buffer));
+	ASSERT_NE(buffer, NULL);
+
+	buffer->fd = fd;
+	buffer->size = size;
+	buffer->mirror = malloc(size);
+	ASSERT_NE(buffer->mirror, NULL);
+
+	buffer->ptr = mmap(NULL, size,
+			   PROT_READ | PROT_WRITE,
+			   MAP_SHARED,
+			   buffer->fd, 0);
+	ASSERT_NE(buffer->ptr, MAP_FAILED);
+
+	/* Initialize data that the device will write to buffer->ptr. */
+	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+		ptr[i] = i;
+
+	/* Simulate a device writing system memory. */
+	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_WRITE, buffer, npages);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(buffer->cpages, npages);
+	ASSERT_EQ(buffer->faults, 1);
+
+	/* Check what the device wrote. */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], i);
+
+	/* Check that the device also wrote the file. */
+	off = lseek(fd, 0, SEEK_SET);
+	ASSERT_EQ(off, 0);
+	len = read(fd, buffer->mirror, size);
+	ASSERT_EQ(len, size);
+	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], i);
+
+	hmm_buffer_free(buffer);
+}
+
+/*
+ * Migrate anonymous memory to device private memory.
+ */
+TEST_F(hmm, migrate)
+{
+	struct hmm_buffer *buffer;
+	unsigned long npages;
+	unsigned long size;
+	unsigned long i;
+	int *ptr;
+	int ret;
+
+	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
+	ASSERT_NE(npages, 0);
+	size = npages << self->page_shift;
+
+	buffer = malloc(sizeof(*buffer));
+	ASSERT_NE(buffer, NULL);
+
+	buffer->fd = -1;
+	buffer->size = size;
+	buffer->mirror = malloc(size);
+	ASSERT_NE(buffer->mirror, NULL);
+
+	buffer->ptr = mmap(NULL, size,
+			   PROT_READ | PROT_WRITE,
+			   MAP_PRIVATE | MAP_ANONYMOUS,
+			   buffer->fd, 0);
+	ASSERT_NE(buffer->ptr, MAP_FAILED);
+
+	/* Initialize buffer in system memory. */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ptr[i] = i;
+
+	/* Migrate memory to device. */
+	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_MIGRATE, buffer, npages);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(buffer->cpages, npages);
+
+	/* Check what the device read. */
+	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], i);
+
+	hmm_buffer_free(buffer);
+}
+
+/*
+ * Migrate anonymous memory to device private memory and fault it back to system
+ * memory.
+ */
+TEST_F(hmm, migrate_fault)
+{
+	struct hmm_buffer *buffer;
+	unsigned long npages;
+	unsigned long size;
+	unsigned long i;
+	int *ptr;
+	int ret;
+
+	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
+	ASSERT_NE(npages, 0);
+	size = npages << self->page_shift;
+
+	buffer = malloc(sizeof(*buffer));
+	ASSERT_NE(buffer, NULL);
+
+	buffer->fd = -1;
+	buffer->size = size;
+	buffer->mirror = malloc(size);
+	ASSERT_NE(buffer->mirror, NULL);
+
+	buffer->ptr = mmap(NULL, size,
+			   PROT_READ | PROT_WRITE,
+			   MAP_PRIVATE | MAP_ANONYMOUS,
+			   buffer->fd, 0);
+	ASSERT_NE(buffer->ptr, MAP_FAILED);
+
+	/* Initialize buffer in system memory. */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ptr[i] = i;
+
+	/* Migrate memory to device. */
+	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_MIGRATE, buffer, npages);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(buffer->cpages, npages);
+
+	/* Check what the device read. */
+	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], i);
+
+	/* Fault pages back to system memory and check them. */
+	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+		ASSERT_EQ(ptr[i], i);
+
+	hmm_buffer_free(buffer);
+}
+
+/*
+ * Try to migrate various memory types to device private memory.
+ */
+TEST_F(hmm2, migrate_mixed)
+{
+	struct hmm_buffer *buffer;
+	unsigned long npages;
+	unsigned long size;
+	int *ptr;
+	unsigned char *p;
+	int ret;
+	int val;
+
+	npages = 6;
+	size = npages << self->page_shift;
+
+	buffer = malloc(sizeof(*buffer));
+	ASSERT_NE(buffer, NULL);
+
+	buffer->fd = -1;
+	buffer->size = size;
+	buffer->mirror = malloc(size);
+	ASSERT_NE(buffer->mirror, NULL);
+
+	/* Reserve a range of addresses. */
+	buffer->ptr = mmap(NULL, size,
+			   PROT_NONE,
+			   MAP_PRIVATE | MAP_ANONYMOUS,
+			   buffer->fd, 0);
+	ASSERT_NE(buffer->ptr, MAP_FAILED);
+	p = buffer->ptr;
+
+	/* Now try to migrate everything to device 1. */
+	ret = hmm_dmirror_cmd(self->fd1, HMM_DMIRROR_MIGRATE, buffer, npages);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(buffer->cpages, 6);
+
+	/* Punch a hole after the first page address. */
+	ret = munmap(buffer->ptr + self->page_size, self->page_size);
+	ASSERT_EQ(ret, 0);
+
+	/* We expect an error if the vma doesn't cover the range. */
+	ret = hmm_dmirror_cmd(self->fd1, HMM_DMIRROR_MIGRATE, buffer, 3);
+	ASSERT_EQ(ret, -EINVAL);
+
+	/* Page 2 will be a read-only zero page. */
+	ret = mprotect(buffer->ptr + 2 * self->page_size, self->page_size,
+				PROT_READ);
+	ASSERT_EQ(ret, 0);
+	ptr = (int *)(buffer->ptr + 2 * self->page_size);
+	val = *ptr + 3;
+	ASSERT_EQ(val, 3);
+
+	/* Page 3 will be read-only. */
+	ret = mprotect(buffer->ptr + 3 * self->page_size, self->page_size,
+				PROT_READ | PROT_WRITE);
+	ASSERT_EQ(ret, 0);
+	ptr = (int *)(buffer->ptr + 3 * self->page_size);
+	*ptr = val;
+	ret = mprotect(buffer->ptr + 3 * self->page_size, self->page_size,
+				PROT_READ);
+	ASSERT_EQ(ret, 0);
+
+	/* Page 4 will be read-write. */
+	ret = mprotect(buffer->ptr + 4 * self->page_size, self->page_size,
+				PROT_READ | PROT_WRITE);
+	ASSERT_EQ(ret, 0);
+	ptr = (int *)(buffer->ptr + 4 * self->page_size);
+	*ptr = val;
+
+	/* Page 5 won't be migrated to device 0 because it's on device 1. */
+	buffer->ptr = p + 5 * self->page_size;
+	ret = hmm_dmirror_cmd(self->fd0, HMM_DMIRROR_MIGRATE, buffer, 1);
+	ASSERT_EQ(ret, -ENOENT);
+	buffer->ptr = p;
+
+	/* Now try to migrate pages 2-3 to device 1. */
+	buffer->ptr = p + 2 * self->page_size;
+	ret = hmm_dmirror_cmd(self->fd1, HMM_DMIRROR_MIGRATE, buffer, 2);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(buffer->cpages, 2);
+	buffer->ptr = p;
+
+	hmm_buffer_free(buffer);
+}
+
+/*
+ * Migrate anonymous memory to device private memory and fault it back to system
+ * memory multiple times.
+ */
+TEST_F(hmm, migrate_multiple)
+{
+	struct hmm_buffer *buffer;
+	unsigned long npages;
+	unsigned long size;
+	unsigned long i;
+	unsigned long c;
+	int *ptr;
+	int ret;
+
+	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
+	ASSERT_NE(npages, 0);
+	size = npages << self->page_shift;
+
+	for (c = 0; c < NTIMES; c++) {
+		buffer = malloc(sizeof(*buffer));
+		ASSERT_NE(buffer, NULL);
+
+		buffer->fd = -1;
+		buffer->size = size;
+		buffer->mirror = malloc(size);
+		ASSERT_NE(buffer->mirror, NULL);
+
+		buffer->ptr = mmap(NULL, size,
+				   PROT_READ | PROT_WRITE,
+				   MAP_PRIVATE | MAP_ANONYMOUS,
+				   buffer->fd, 0);
+		ASSERT_NE(buffer->ptr, MAP_FAILED);
+
+		/* Initialize buffer in system memory. */
+		for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+			ptr[i] = i;
+
+		/* Migrate memory to device. */
+		ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_MIGRATE, buffer,
+				      npages);
+		ASSERT_EQ(ret, 0);
+		ASSERT_EQ(buffer->cpages, npages);
+
+		/* Check what the device read. */
+		for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+			ASSERT_EQ(ptr[i], i);
+
+		/* Fault pages back to system memory and check them. */
+		for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+			ASSERT_EQ(ptr[i], i);
+
+		hmm_buffer_free(buffer);
+	}
+}
+
+/*
+ * Read anonymous memory multiple times.
+ */
+TEST_F(hmm, anon_read_multiple)
+{
+	struct hmm_buffer *buffer;
+	unsigned long npages;
+	unsigned long size;
+	unsigned long i;
+	unsigned long c;
+	int *ptr;
+	int ret;
+
+	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
+	ASSERT_NE(npages, 0);
+	size = npages << self->page_shift;
+
+	for (c = 0; c < NTIMES; c++) {
+		buffer = malloc(sizeof(*buffer));
+		ASSERT_NE(buffer, NULL);
+
+		buffer->fd = -1;
+		buffer->size = size;
+		buffer->mirror = malloc(size);
+		ASSERT_NE(buffer->mirror, NULL);
+
+		buffer->ptr = mmap(NULL, size,
+				   PROT_READ | PROT_WRITE,
+				   MAP_PRIVATE | MAP_ANONYMOUS,
+				   buffer->fd, 0);
+		ASSERT_NE(buffer->ptr, MAP_FAILED);
+
+		/* Initialize buffer in system memory. */
+		for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+			ptr[i] = i + c;
+
+		/* Simulate a device reading system memory. */
+		ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_READ, buffer,
+				      npages);
+		ASSERT_EQ(ret, 0);
+		ASSERT_EQ(buffer->cpages, npages);
+		ASSERT_EQ(buffer->faults, 1);
+
+		/* Check what the device read. */
+		for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+			ASSERT_EQ(ptr[i], i + c);
+
+		hmm_buffer_free(buffer);
+	}
+}
+
+void *unmap_buffer(void *p)
+{
+	struct hmm_buffer *buffer = p;
+
+	/* Delay for a bit and then unmap buffer while it is being read. */
+	hmm_nanosleep(hmm_random() % 32000);
+	munmap(buffer->ptr + buffer->size / 2, buffer->size / 2);
+	buffer->ptr = NULL;
+
+	return NULL;
+}
+
+/*
+ * Try reading anonymous memory while it is being unmapped.
+ */
+TEST_F(hmm, anon_teardown)
+{
+	unsigned long npages;
+	unsigned long size;
+	unsigned long c;
+	void *ret;
+
+	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
+	ASSERT_NE(npages, 0);
+	size = npages << self->page_shift;
+
+	for (c = 0; c < NTIMES; ++c) {
+		pthread_t thread;
+		struct hmm_buffer *buffer;
+		unsigned long i;
+		int *ptr;
+		int rc;
+
+		buffer = malloc(sizeof(*buffer));
+		ASSERT_NE(buffer, NULL);
+
+		buffer->fd = -1;
+		buffer->size = size;
+		buffer->mirror = malloc(size);
+		ASSERT_NE(buffer->mirror, NULL);
+
+		buffer->ptr = mmap(NULL, size,
+				   PROT_READ | PROT_WRITE,
+				   MAP_PRIVATE | MAP_ANONYMOUS,
+				   buffer->fd, 0);
+		ASSERT_NE(buffer->ptr, MAP_FAILED);
+
+		/* Initialize buffer in system memory. */
+		for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+			ptr[i] = i + c;
+
+		rc = pthread_create(&thread, NULL, unmap_buffer, buffer);
+		ASSERT_EQ(rc, 0);
+
+		/* Simulate a device reading system memory. */
+		rc = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_READ, buffer,
+				     npages);
+		if (rc == 0) {
+			ASSERT_EQ(buffer->cpages, npages);
+			ASSERT_EQ(buffer->faults, 1);
+
+			/* Check what the device read. */
+			for (i = 0, ptr = buffer->mirror;
+			     i < size / sizeof(*ptr);
+			     ++i)
+				ASSERT_EQ(ptr[i], i + c);
+		}
+
+		pthread_join(thread, &ret);
+		hmm_buffer_free(buffer);
+	}
+}
+
+/*
+ * Test memory snapshot without faulting in pages accessed by the device.
+ */
+TEST_F(hmm2, snapshot)
+{
+	struct hmm_buffer *buffer;
+	unsigned long npages;
+	unsigned long size;
+	int *ptr;
+	unsigned char *p;
+	unsigned char *m;
+	int ret;
+	int val;
+
+	npages = 7;
+	size = npages << self->page_shift;
+
+	buffer = malloc(sizeof(*buffer));
+	ASSERT_NE(buffer, NULL);
+
+	buffer->fd = -1;
+	buffer->size = size;
+	buffer->mirror = malloc(npages);
+	ASSERT_NE(buffer->mirror, NULL);
+
+	/* Reserve a range of addresses. */
+	buffer->ptr = mmap(NULL, size,
+			   PROT_NONE,
+			   MAP_PRIVATE | MAP_ANONYMOUS,
+			   buffer->fd, 0);
+	ASSERT_NE(buffer->ptr, MAP_FAILED);
+	p = buffer->ptr;
+
+	/* Punch a hole after the first page address. */
+	ret = munmap(buffer->ptr + self->page_size, self->page_size);
+	ASSERT_EQ(ret, 0);
+
+	/* Page 2 will be read-only zero page. */
+	ret = mprotect(buffer->ptr + 2 * self->page_size, self->page_size,
+				PROT_READ);
+	ASSERT_EQ(ret, 0);
+	ptr = (int *)(buffer->ptr + 2 * self->page_size);
+	val = *ptr + 3;
+	ASSERT_EQ(val, 3);
+
+	/* Page 3 will be read-only. */
+	ret = mprotect(buffer->ptr + 3 * self->page_size, self->page_size,
+				PROT_READ | PROT_WRITE);
+	ASSERT_EQ(ret, 0);
+	ptr = (int *)(buffer->ptr + 3 * self->page_size);
+	*ptr = val;
+	ret = mprotect(buffer->ptr + 3 * self->page_size, self->page_size,
+				PROT_READ);
+	ASSERT_EQ(ret, 0);
+
+	/* Page 4-6 will be read-write. */
+	ret = mprotect(buffer->ptr + 4 * self->page_size, 3 * self->page_size,
+				PROT_READ | PROT_WRITE);
+	ASSERT_EQ(ret, 0);
+	ptr = (int *)(buffer->ptr + 4 * self->page_size);
+	*ptr = val;
+
+	/* Page 5 will be migrated to device 0. */
+	buffer->ptr = p + 5 * self->page_size;
+	ret = hmm_dmirror_cmd(self->fd0, HMM_DMIRROR_MIGRATE, buffer, 1);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(buffer->cpages, 1);
+
+	/* Page 6 will be migrated to device 1. */
+	buffer->ptr = p + 6 * self->page_size;
+	ret = hmm_dmirror_cmd(self->fd1, HMM_DMIRROR_MIGRATE, buffer, 1);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(buffer->cpages, 1);
+
+	/* Simulate a device snapshotting CPU pagetables. */
+	buffer->ptr = p;
+	ret = hmm_dmirror_cmd(self->fd0, HMM_DMIRROR_SNAPSHOT, buffer, npages);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(buffer->cpages, npages);
+
+	/* Check what the device saw. */
+	m = buffer->mirror;
+	ASSERT_EQ(m[0], HMM_DMIRROR_PROT_NONE);
+	ASSERT_EQ(m[1], HMM_DMIRROR_PROT_NONE);
+	ASSERT_EQ(m[2], HMM_DMIRROR_PROT_ZERO | HMM_DMIRROR_PROT_READ);
+	ASSERT_EQ(m[3], HMM_DMIRROR_PROT_READ);
+	ASSERT_EQ(m[4], HMM_DMIRROR_PROT_WRITE);
+	ASSERT_EQ(m[5], HMM_DMIRROR_PROT_DEV_PRIVATE_LOCAL |
+			HMM_DMIRROR_PROT_WRITE);
+	ASSERT_EQ(m[6], HMM_DMIRROR_PROT_DEV_PRIVATE_REMOTE |
+			HMM_DMIRROR_PROT_WRITE);
+
+	hmm_buffer_free(buffer);
+}
+
+TEST_HARNESS_MAIN
diff --git a/tools/testing/selftests/vm/run_vmtests b/tools/testing/selftests/vm/run_vmtests
index 951c507a27f7..634cfefdaffd 100755
--- a/tools/testing/selftests/vm/run_vmtests
+++ b/tools/testing/selftests/vm/run_vmtests
@@ -227,4 +227,20 @@  else
 	exitcode=1
 fi
 
+echo "------------------------------------"
+echo "running HMM smoke test"
+echo "------------------------------------"
+./test_hmm.sh smoke
+ret_val=$?
+
+if [ $ret_val -eq 0 ]; then
+	echo "[PASS]"
+elif [ $ret_val -eq $ksft_skip ]; then
+	echo "[SKIP]"
+	exitcode=$ksft_skip
+else
+	echo "[FAIL]"
+	exitcode=1
+fi
+
 exit $exitcode
diff --git a/tools/testing/selftests/vm/test_hmm.sh b/tools/testing/selftests/vm/test_hmm.sh
new file mode 100755
index 000000000000..461e4a99a362
--- /dev/null
+++ b/tools/testing/selftests/vm/test_hmm.sh
@@ -0,0 +1,97 @@ 
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) 2018 Uladzislau Rezki (Sony) <urezki@gmail.com>
+#
+# This is a test script for the kernel test driver to analyse vmalloc
+# allocator. Therefore it is just a kernel module loader. You can specify
+# and pass different parameters in order to:
+#     a) analyse performance of vmalloc allocations;
+#     b) stressing and stability check of vmalloc subsystem.
+
+TEST_NAME="test_hmm"
+DRIVER="test_hmm"
+
+# 1 if fails
+exitcode=1
+
+# Kselftest framework requirement - SKIP code is 4.
+ksft_skip=4
+
+check_test_requirements()
+{
+	uid=$(id -u)
+	if [ $uid -ne 0 ]; then
+		echo "$0: Must be run as root"
+		exit $ksft_skip
+	fi
+
+	if ! which modprobe > /dev/null 2>&1; then
+		echo "$0: You need modprobe installed"
+		exit $ksft_skip
+	fi
+
+	if ! modinfo $DRIVER > /dev/null 2>&1; then
+		echo "$0: You must have the following enabled in your kernel:"
+		echo "CONFIG_TEST_HMM=m"
+		exit $ksft_skip
+	fi
+}
+
+load_driver()
+{
+	modprobe $DRIVER > /dev/null 2>&1
+	if [ $? == 0 ]; then
+		major=$(awk "\$2==\"HMM_DMIRROR\" {print \$1}" /proc/devices)
+		mknod /dev/hmm_dmirror0 c $major 0
+		mknod /dev/hmm_dmirror1 c $major 1
+	fi
+}
+
+unload_driver()
+{
+	modprobe -r $DRIVER > /dev/null 2>&1
+	rm -f /dev/hmm_dmirror?
+}
+
+run_smoke()
+{
+	echo "Running smoke test. Note, this test provides basic coverage."
+
+	load_driver
+	./hmm-tests
+	unload_driver
+}
+
+usage()
+{
+	echo -n "Usage: $0"
+	echo
+	echo "Example usage:"
+	echo
+	echo "# Shows help message"
+	echo "./${TEST_NAME}.sh"
+	echo
+	echo "# Smoke testing"
+	echo "./${TEST_NAME}.sh smoke"
+	echo
+	exit 0
+}
+
+function run_test()
+{
+	if [ $# -eq 0 ]; then
+		usage
+	else
+		if [ "$1" = "smoke" ]; then
+			run_smoke
+		else
+			usage
+		fi
+	fi
+}
+
+check_test_requirements
+run_test $@
+
+exit 0